System and method for detecting an intruder using impulse radio technology

ABSTRACT

An intrusion detection system and method are provided that can utilize impulse radio technology to detect when an intruder has entered a protection zone. In addition, the intrusion detection system and method can utilize impulse radio technology to determine a location of the intruder within the protection zone and also track the movement of the intruder within the protection zone. Moreover, the intrusion detection system and method can utilize impulse radio technology to create a specially shaped protection zone before trying to detect when and where the intruder has penetrated and moved within the protection zone.

This application is a continuation application of U.S. patentapplication Ser. No. 09/952,206, filed Sep. 14, 2001 now U.S. Pat. No.6,614,384, which claims the benefit of U.S. Provisional Application Ser.No. 60/232,562, filed on Sep. 14, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to the security field and, inparticular, to a system and method capable of using impulse radiotechnology to detect when an intruder has entered a protection zone andwhere in the protection zone the intruder is currently located.

2. Description of Related Art

Today there are many types of intrusion detection systems that candetect and signal an alarm if a person enters a protection zone. Onetype of an intrusion detection system uses sensors to detect an intruderwhere the sensors are placed on the doors, windows or any opening of abuilding that can be breached by the intruder. Thus, if an intruderopens a door or window a circuit in a sensor is interrupted and then theintrusion detection system sounds an alarm and/or alerts remote securitypersonnel. This type of intrusion detection system can be employed onlywhere a building or structure is available to support the wiring for thesensors.

Another type of intrusion detection system may use invisible beams oflight, visible beams of light or narrow radar beams to effectively forma fence around a protection zone. Thus, if an intruder interrupts one ofthe beams then the intrusion detection system sounds an alarm and/oralerts remote security personnel. Unfortunately, if the intruderpenetrates the fence without triggering the alarm then detection of thatintruder by the intrusion detection system is unlikely.

Yet another type of intrusion detection system may use radar orultrasonic energy throughout the area in the protection zone. Thus, ifan intruder moves within the protection zone a Doppler shift in theradar or ultrasonic energy may be detected by the intrusion detectionsystem which then sounds an alarm and/or alerts remote securitypersonnel. Unfortunately, all of these intrusion detection systems andother well known intrusion detection systems can be easily jammed,hacked, spoofed or otherwise defeated by intruders. For instance, a slowmoving intruder can trick the traditional intrusion detection systemthat uses narrow radar beams to form a fence around a protection zone.Accordingly, there is a need for an intrusion detection system andmethod that is essentially spoof-proof or very difficult for an intruderto defeat. This need and other needs are solved by the intrusiondetection system and method of the present invention.

BRIEF DESCRIPTION OF THE INVENTION

The present invention includes an intrusion detection system and methodthat can utilize impulse radio technology to detect when an intruder hasentered a protection zone. In addition, the intrusion detection systemand method can utilize impulse radio technology to determine a locationof the intruder within the protection zone and also track the movementof the intruder within the protection zone. Moreover, the intrusiondetection system and method can utilize impulse radio technology tocreate a specially shaped protection zone before trying to detect whenand where the intruder has penetrated and moved within the protectionzone.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be had byreference to the following detailed description when taken inconjunction with the accompanying drawings wherein:

FIG. 1A illustrates a representative Gaussian Monocycle waveform in thetime domain;

FIG. 1B illustrates the frequency domain amplitude of the GaussianMonocycle of FIG. 1A;

FIG. 1C represents the second derivative of the Gaussian Monocycle ofFIG. 1A;

FIG. 1D represents the third derivative of the Gaussian Monocycle ofFIG. 1A;

FIG. 1E represents the Correlator Output vs. the Relative Delay in areal data pulse;

FIG. 1F graphically depicts the frequency plot of the Gaussian family ofthe Gaussian Pulse and the first, second, and third derivative.

FIG. 2A illustrates a pulse train comprising pulses as in FIG. 1A;

FIG. 2B illustrates the frequency domain amplitude of the waveform ofFIG. 2A;

FIG. 2C illustrates the pulse train spectrum;

FIG. 2D is a plot of the Frequency vs. Energy Plot and points out thecoded signal energy spikes;

FIG. 3 illustrates the cross-correlation of two codes graphically asCoincidences vs. Time Offset;

FIGS. 4A-4E graphically illustrate five modulation techniques toinclude: Early-Late Modulation; One of Many Modulation; Flip Modulation;Quad Flip Modulation; and Vector Modulation;

FIG. 5A illustrates representative signals of an interfering signal, acoded received pulse train and a coded reference pulse train;

FIG. 5B depicts a typical geometrical configuration giving rise tomultipath received signals;

FIG. 5C illustrates exemplary multipath signals in the time domain;

FIGS. 5D-5F illustrate a signal plot of various multipath environments.

FIG. 5G illustrates the Rayleigh fading curve associated withnon-impulse radio transmissions in a multipath environment.

FIG. 5H illustrates a plurality of multipaths with a plurality ofreflectors from a transmitter to a receiver.

FIG. 5I graphically represents signal strength as volts vs. time in adirect path and multipath environment.

FIG. 6 illustrates a representative impulse radio transmitter functionaldiagram;

FIG. 7 illustrates a representative impulse radio receiver functionaldiagram;

FIG. 8A illustrates a representative received pulse signal at the inputto the correlator;

FIG. 8B illustrates a sequence of representative impulse signals in thecorrelation process;

FIG. 8C illustrates the output of the correlator for each of the timeoffsets of FIG. 8B.

FIG. 9 illustrates an exemplary block diagram of an ultra-widebandscanning receiver that could be used in the present invention.

FIG. 10 illustrates an exemplary block diagram of an ultra-widebandscanning transmitter that could be used in the present invention.

FIG. 11 illustrates a diagram of the basic components of a firstembodiment of the intrusion detection system in accordance with thepresent invention (see also FIG. 14).

FIG. 12 illustrates a diagram of the basic components of a secondembodiment of the intrusion detection system in accordance with thepresent invention (see also FIG. 17).

FIG. 13 illustrates an example of a specially shaped protection zoneassociated with a third embodiment in accordance with the presentinvention (see also FIG. 20).

FIG. 14 illustrates in greater detail a diagram of the basic componentsof the first embodiment of the intrusion detection system in accordancewith the present invention.

FIGS. 15a-15 b illustrate an exemplary first waveform and an exemplarysecond waveform that could be generated by a receiving impulse radiounit shown in FIG. 14.

FIG. 16 illustrates a flowchart of the basic steps of a first embodimentof the preferred method in accordance with the present invention.

FIG. 17 illustrates in greater detail a diagram of the basic componentsof a second embodiment of the intrusion detection system in accordancewith the present invention.

FIGS. 18a-18 b illustrate exemplary first waveforms and exemplary secondwaveforms that could be generated by three different receiving impulseradio units shown in FIG. 17.

FIGS. 19a-19 b illustrates a flowchart of the basic steps of a secondembodiment of the preferred method in accordance with the presentinvention.

FIG. 20 illustrates in greater detail a diagram of the basic componentsof a third embodiment of the intrusion detection system in accordancewith the present invention.

FIGS. 21a-21 b illustrates a flowchart of the basic steps of a thirdembodiment of the preferred method in accordance with the presentinvention.

FIG. 22 illustrates a diagram of the intrusion detection systemincorporating one or more directive antennas.

DETAILED DESCRIPTION OF THE INVENTION

The present invention includes an intrusion detection system and methodthat can utilize impulse radio technology to detect when an intruder hasentered a protection zone. In addition, the intrusion detection systemand method can utilize impulse radio technology to determine a locationof the intruder within the protection zone and also to track themovement of the intruder within the protection zone. Moreover, theintrusion detection system and method can utilize impulse radiotechnology to create a specially shaped protection zone before trying todetect when and where the intruder has penetrated and moved within theprotection zone. Many of these capabilities are possible, due to the useof an emerging, revolutionary ultra wideband technology (UWB) calledimpulse radio technology (also known as impulse radio) which is asignificant improvement over conventional radar technology andconventional radio technology.

Impulse radio has been described in a series of patents, including U.S.Pat. No. 4,641,317 (issued Feb. 3, 1987), U.S. Pat. No. 4,813,057(issued Mar. 14, 1989), U.S. Pat. No. 4,979,186 (issued Dec. 18, 1990)and U.S. Pat. No. 5,363,108 (issued Nov. 8, 1994) to Larry W. Fullerton.A second generation of impulse radio patents includes U.S. Pat. No.5,677,927 (issued Oct. 14, 1997), U.S. Pat. No. 5,687,169 (issued Nov.11, 1997), U.S. Pat. No. 5,764,696 (issued Jun. 9, 1998), and U.S. Pat.No. 5,832,035 (issued Nov. 3, 1998) to Fullerton et al.

Uses of impulse radio systems are described in U.S. Pat. No. 6,177,903,titled, “System and Method for Intrusion Detection using a Time DomainRadar Array” and U.S. Pat. No. 6,218,979, titled, “Wide Area Time DomainRadar Array” both filed on Jun. 14, 1999 both of which are assigned tothe assignee of the present invention. The above patent documents areincorporated herein by reference.

This section provides an overview of impulse radio technology andrelevant aspects of communications theory. It is provided to assist thereader with understanding the present invention and should not be usedto limit the scope of the present invention. It should be understoodthat the terminology ‘impulse radio’ is used primarily for historicalconvenience and that the terminology can be generally interchanged withthe terminology ‘impulse communications system, ultra-wideband system,or ultra-wideband communication systems’. Furthermore, it should beunderstood that the described impulse radio technology is generallyapplicable to various other impulse system applications including butnot limited to impulse radar systems and impulse positioning systems.Accordingly, the terminology ‘impulse radio’ can be generallyinterchanged with the terminology ‘impulse transmission system andimpulse reception system.’

Impulse radio refers to a radio system based on short, low duty-cyclepulses. An ideal impulse radio waveform is a short Gaussian monocycle.As the name suggests, this waveform attempts to approach one cycle ofradio frequency (RF) energy at a desired center frequency. Due toimplementation and other spectral limitations, this waveform may bealtered significantly in practice for a given application. Manywaveforms having very broad, or wide, spectral bandwidth approximate aGaussian shape to a useful degree.

Impulse radio can use many types of modulation, including amplitudemodulation, phase modulation, frequency modulation, time-shiftmodulation (also referred to as pulse-position modulation orpulse-interval modulation) and M-ary versions of these. In thisdocument, the time-shift modulation method is often used as anillustrative example. However, someone skilled in the art will recognizethat alternative modulation approaches may, in some instances, be usedinstead of or in combination with the time-shift modulation approach.

In impulse radio communications, inter-pulse spacing may be heldconstant or may be varied on a pulse-by-pulse basis by information, acode, or both. Generally, conventional spread spectrum systems employcodes to spread the normally narrow band information signal over arelatively wide band of frequencies. A conventional spread spectrumreceiver correlates these signals to retrieve the original informationsignal. In impulse radio communications, codes are not typically usedfor energy spreading because the monocycle pulses themselves have aninherently wide bandwidth. Codes are more commonly used forchannelization, energy smoothing in the frequency domain, resistance tointerference, and reducing the interference potential to nearbyreceivers. Such codes are commonly referred to as time-hopping codes orpseudo-noise (PN) codes since their use typically causes inter-pulsespacing to have a seemingly random nature. PN codes may be generated bytechniques other than pseudorandom code generation. Additionally, pulsetrains having constant, or uniform, pulse spacing are commonly referredto as uncoded pulse trains. A pulse train with uniform pulse spacing,however, may be described by a code that specifies non-temporal, i.e.,non-time related, pulse characteristics.

In impulse radio communications utilizing time-shift modulation,information comprising one or more bits of data typically time-positionmodulates a sequence of pulses. This yields a modulated, coded timingsignal that comprises a train of pulses from which a typical impulseradio receiver employing the same code may demodulate and, if necessary,coherently integrate pulses to recover the transmitted information.

The impulse radio receiver is typically a direct conversion receiverwith a cross correlator front-end that coherently converts anelectromagnetic pulse train of monocycle pulses to a baseband signal ina single stage. The baseband signal is the basic information signal forthe impulse radio communications system. A subcarrier may also beincluded with the baseband signal to reduce the effects of amplifierdrift and low frequency noise. Typically, the subcarrier alternatelyreverses modulation according to a known pattern at a rate faster thanthe data rate. This same pattern is used to reverse the process andrestore the original data pattern just before detection. This methodpermits alternating current (AC) coupling of stages, or equivalentsignal processing, to eliminate direct current (DC) drift and errorsfrom the detection process. This method is described in more detail inU.S. Pat. No. 5,677,927 to Fullerton et al.

Waveforms

Impulse transmission systems are based on short, low duty-cycle pulses.Different pulse waveforms, or pulse types, may be employed toaccommodate requirements of various applications. Typical pulse typesinclude a Gaussian pulse, pulse doublet (also referred to as a Gaussianmonocycle), pulse triplet, and pulse quadlet as depicted in FIGS. 1Athrough 1D, respectively. An actual received waveform that closelyresembles the theoretical pulse quadlet is shown in FIG. 1E. A pulsetype may also be a wavelet set produced by combining two or more pulsewaveforms (e.g., a doublet/triplet wavelet set). These different pulsetypes may be produced by methods described in the patent documentsreferenced above or by other methods, as persons skilled in the artwould understand.

For analysis purposes, it is convenient to model pulse waveforms in anideal manner. For example, the transmitted waveform produced bysupplying a step function into an ultra-wideband antenna may be modeledas a Gaussian monocycle. A Gaussian monocycle (normalized to a peakvalue of 1) may be described by:${f_{mono}(t)} = {\sqrt{}\left( \frac{t}{\sigma} \right)^{\frac{- t^{2}}{2\sigma^{2}}}}$

where σ is a time scaling parameter, t is time, and e is the naturallogarithm base.

The power special density of the Gaussian monocycle is shown in FIG. 1F,along with spectrums for the Gaussian pulse, triplet, and quadlet. Thecorresponding equation for the Gaussian monocycle is:${F_{mono}(f)} = {\left( {2\pi} \right)^{\frac{3}{2}}\sigma \quad f\quad ^{{- 2}{({\pi \quad \sigma \quad f})}^{2}}}$

The center frequency (f_(c)), or frequency of peak spectral density, ofthe Gaussian monocycle is: $f_{c} = \frac{1}{2\pi \quad \sigma}$

It should be noted that the output of an ultra-wideband antenna isessentially equal to the derivative of its input. Accordingly, since thepulse doublet, pulse triplet, and pulse quadlet are the first, second,and third derivatives of the Gaussian pulse, in an ideal model, anantenna receiving a Gaussian pulse will transmit a Gaussian monocycleand an antenna receiving a Gaussian monocycle will provide a pulsetriplet.

Pulse Trains

Impulse transmission systems may communicate one or more data bits witha single pulse; however, typically each data bit is communicated using asequence of pulses, known as a pulse train. As described in detail inthe following example system, the impulse radio transmitter produces andoutputs a train of pulses for each bit of information. FIGS. 2A and 2Bare illustrations of the output of a typical 10 megapulses per second(Mpps) system with uncoded, unmodulated pulses, each having a width of0.5 nanoseconds (ns). FIG. 2A shows a time domain representation of thepulse train output. FIG. 2B illustrates that the result of the pulsetrain in the frequency domain is to produce a spectrum comprising a setof comb lines spaced at the frequency of the 10 Mpps pulse repetitionrate. When the full spectrum is shown, as in FIG. 2C, the envelope ofthe comb line spectrum corresponds to the curve of the single Gaussianmonocycle spectrum in FIG. 1F. For this simple uncoded case, the powerof the pulse train is spread among roughly two hundred comb lines. Eachcomb line thus has a small fraction of the total power and presents muchless of an interference problem to a receiver sharing the band. It canalso be observed from FIG. 2A that impulse transmission systemstypically have very low average duty cycles, resulting in average powerlower than peak power. The duty cycle of the signal in FIG. 2A is 0.5%,based on a 0.5 ns pulse duration in a 100 ns interval.

The signal of an uncoded, unmodulated pulse train may be expressed:${s(t)} = {\left( {- 1} \right)^{f}a{\sum\limits_{j}^{\quad}\quad {\omega \left( {{{ct} - {j\quad T_{f}}},b} \right)}}}$

where j is the index of a pulse within a pulse train, (−1)^(f) ispolarity (+/−), a is pulse amplitude, b is pulse type, c is pulse width,ω(t,b) is the normalized pulse waveform, and T_(f) is pulse repetitiontime.

The energy spectrum of a pulse train signal over a frequency bandwidthof interest may be determined by summing the phasors of the pulses ateach frequency, using the following equation:${A(\omega)} = {{\sum\limits_{i = 1}^{n}\quad \frac{^{j\quad \Delta \quad t}}{n}}}$

where A(ω) is the amplitude of the spectral response at a givenfrequency . . . ω is the frequency being analyzed (2πf), Δt is therelative time delay of each pulse from the start of time period, and nis the total number of pulses in the pulse train.

A pulse train can also be characterized by its autocorrelation andcross-correlation properties. Autocorrelation properties pertain to thenumber of pulse coincidences (i.e., simultaneous arrival of pulses) thatoccur when a pulse train is correlated against an instance of itselfthat is offset in time. Of primary importance is the ratio of the numberof pulses in the pulse train to the maximum number of coincidences thatoccur for any time offset across the period of the pulse train. Thisratio is commonly referred to as the main-lobe-to-side-lobe ratio, wherethe greater the ratio, the easier it is to acquire and track a signal.

Cross-correlation properties involve the potential for pulses from twodifferent signals simultaneously arriving, or coinciding, at a receiver.Of primary importance are the maximum and average numbers of pulsecoincidences that may occur between two pulse trains. As the number ofcoincidences increases, the propensity for data errors increases.Accordingly, pulse train cross-correlation properties are used indetermining channelization capabilities of impulse transmission systems(i.e., the ability to simultaneously operate within close proximity).

Coding

Specialized coding techniques can be employed to specify temporal and/ornon-temporal pulse characteristics to produce a pulse train havingcertain spectral and/or correlation properties. For example, byemploying a PN code to vary inter-pulse spacing, the energy in the comblines presented in FIG. 2B can be distributed to other frequencies asdepicted in FIG. 2D, thereby decreasing the peak spectral density withina bandwidth of interest. Note that the spectrum retains certainproperties that depend on the specific (temporal) PN code used. Spectralproperties can be similarly affected by using non-temporal coding (e.g.,inverting certain pulses).

Coding provides a method of establishing independent communicationchannels. Specifically, families of codes can be designed such that thenumber of pulse coincidences between pulse trains produced by any twocodes will be minimal. For example, FIG. 3 depicts cross-correlationproperties of two codes that have no more than four coincidences for anytime offset. Generally, keeping the number of pulse collisions minimalrepresents a substantial attenuation of the unwanted signal.

Coding can also be used to facilitate signal acquisition. For example,coding techniques can be used to produce pulse trains with a desirablemain-lobe-to-side-lobe ratio. In addition, coding can be used to reduceacquisition algorithm search space.

Coding methods for specifying temporal and non-temporal pulsecharacteristics are described in commonly owned, co-pending applicationstitled “A Method and Apparatus for Positioning Pulses in Time,”application Ser. No. 09/592,249, and “A Method for SpecifyingNon-Temporal Pulse Characteristics,” application Ser. No. 09/592,250 nowabandoned, both filed Jun. 12, 2000, and both of which are incorporatedherein by reference.

Typically, a code consists of a number of code elements having integeror floating-point values. A code element value may specify a singlepulse characteristic or may be subdivided into multiple components, eachspecifying a different pulse characteristic. Code element or codecomponent values typically map to a pulse characteristic value layoutthat may be fixed or non-fixed and may involve value ranges, discretevalues, or a combination of value ranges and discrete values. A valuerange layout specifies a range of values that is divided into componentsthat are each subdivided into subcomponents, which can be furthersubdivided, as desired. In contrast, a discrete value layout involvesuniformly or non-uniformly distributed discrete values. A non-fixedlayout (also referred to as a delta layout) involves delta valuesrelative to some reference value. Fixed and non-fixed layouts, andapproaches for mapping code element/component values, are described inco-owned, co-pending applications, titled “Method for Specifying PulseCharacteristics using Codes,” application Ser. No. 09/592,290, nowabandoned, and “A Method and Apparatus for Mapping Pulses to a Non-FixedLayout,” application Ser. No. 09/591,691, now abandoned both filed onJun. 12, 2000, both of which are incorporated herein by reference.

A fixed or non-fixed characteristic value layout may include anon-allowable region within which a pulse characteristic value isdisallowed. A method for specifying non-allowable regions is describedin co-owned, co-pending application titled “A Method for SpecifyingNon-Allowable Pulse Characteristics,” application Ser. No. 09/592,289,filed Jun. 12, 2000, and incorporated herein by reference. A relatedmethod that conditionally positions pulses depending on whether codeelements map to non-allowable regions is described in co-owned,co-pending application, titled “A Method and Apparatus for PositioningPulses Using a Layout having Non-Allowable Regions,” application Ser.No. 09/592,248 filed Jun. 12, 2000, and incorporated herein byreference.

The signal of a coded pulse train can be generally expressed by:${S_{tr}^{(k)}(t)} = {\sum\limits_{j}^{\quad}\quad {\left( {- 1} \right)^{f_{j}^{(k)}}a_{j}^{(k)}{\omega \left( {{{c_{j}^{(k)}t} - T_{j}^{(k)}},b_{j}^{(k)}} \right)}}}$

where k is the index of a transmitter, j is the index of a pulse withinits pulse train, (−1)f_(j) ^((k)), a_(j) ^((k)), b_(j) ^((k)), c_(j)^((k)), and ω(t,b_(j) ^((k))) are the coded polarity, pulse amplitude,pulse type, pulse width, and normalized pulse waveform of the jth pulseof the kth transmitter, and T_(j) ^((k)) is the coded time shift of thejth pulse of the kth transmitter. Note: When a given non-temporalcharacteristic does not vary (i.e., remains constant for all pulses), itbecomes a constant in front of the summation sign.

Various numerical code generation methods can be employed to producecodes having certain correlation and spectral properties. Such codestypically fall into one of two categories: designed codes andpseudorandom codes. A designed code may be generated using a quadraticcongruential, hyperbolic congruential, linear congruential, Costasarray, or other such numerical code generation technique designed togenerate codes having certain correlation properties. A pseudorandomcode may be generated using a computer's random number generator, binaryshift-register(s) mapped to binary words, a chaotic code generationscheme, or the like. Such ‘random-like’ codes are attractive for certainapplications since they tend to spread spectral energy over multiplefrequencies while having ‘good enough’ correlation properties, whereasdesigned codes may have superior correlation properties but possess lesssuitable spectral properties. Detailed descriptions of numerical codegeneration techniques are included in a co-owned, co-pending patentapplication titled “A Method and Apparatus for Positioning Pulses inTime,” application Ser. No. 09/592,248, filed Jun. 12, 2000, andincorporated herein by reference.

It may be necessary to apply predefined criteria to determine whether agenerated code, code family, or a subset of a code is acceptable for usewith a given UWB application. Criteria may include correlationproperties, spectral properties, code length, non-allowable regions,number of code family members, or other pulse characteristics. A methodfor applying predefined criteria to codes is described in co-owned,co-pending application, titled “A Method and Apparatus for SpecifyingPulse Characteristics using a Code that Satisfies Predefined Criteria,”application Ser. No. 09/592,288, filed Jun. 12, 2000, now U.S. Pat. No.6,636,566, and incorporated herein by reference.

In some applications, it may be desirable to employ a combination ofcodes. Codes may be combined sequentially, nested, or sequentiallynested, and code combinations may be repeated. Sequential codecombinations typically involve switching from one code to the next afterthe occurrence of some event and may also be used to support multicastcommunications. Nested code combinations may be employed to producepulse trains having desirable correlation and spectral properties. Forexample, a designed code may be used to specify value range componentswithin a layout and a nested pseudorandom code may be used to randomlyposition pulses within the value range components. With this approach,correlation properties of the designed code are maintained since thepulse positions specified by the nested code reside within the valuerange components specified by the designed code, while the randompositioning of the pulses within the components results in particularspectral properties. A method for applying code combinations isdescribed in co-owned, co-pending application, titled “A Method andApparatus for Applying Codes Having Pre-Defined Properties,” applicationSer. No. 09/591,690, now U.S. Pat. No. 6,671,310, filed Jun. 12, 2000,and incorporated herein by reference.

Modulation

Various aspects of a pulse waveform may be modulated to conveyinformation and to further minimize structure in the resulting spectrum.Amplitude modulation, phase modulation, frequency modulation, time-shiftmodulation and M-ary versions of these were proposed in U.S. Pat. No.5,677,927 to Fullerton et al., previously incorporated by reference.Time-shift modulation can be described as shifting the position of apulse either forward or backward in time relative to a nominal coded (oruncoded) time position in response to an information signal. Thus, eachpulse in a train of pulses is typically delayed a different amount fromits respective time base clock position by an individual code delayamount plus a modulation time shift. This modulation time shift isnormally very small relative to the code shift. In a 10 Mpps system witha center frequency of 2 GHz, for example, the code may command pulseposition variations over a range of 100 ns, whereas, the informationmodulation may shift the pulse position by 150 ps. This two-state‘early-late’ form of time shift modulation is depicted in FIG. 4A.

A pulse train with conventional ‘early-late’ time-shift modulation canbe expressed:${s_{tr}^{(k)}(t)} = {\sum\limits_{j}^{\quad}\quad {\left( {- 1} \right)^{f_{j}^{(k)}}a_{j}^{(k)}{\omega \left( {{{c_{j}^{(k)}t} - T_{j}^{(k)} - {\delta \quad d_{\lbrack{j/N_{s}}\rbrack}^{(k)}}},b_{j}^{(k)}} \right)}}}$

where k is the index of a transmitter, j is the index of a pulse withinits pulse train, (−1)f_(j) ^((k)), a_(j) ^((k)), b_(j) ^((k)), c_(j)^((k)), and ω(t,b_(j) ^((k))) are the coded polarity, pulse amplitude,pulse type, pulse width, and normalized pulse waveform of the jth pulseof the kth transmitter, T_(j) ^((k)) is the coded time shift of the jthpulse of the kth transmitter, δ is the time shift added when thetransmitted symbol is 1 (instead of 0), d^((k)) is the data (i.e., 0or 1) transmitted by the kth transmitter, and N_(s) is the number ofpulses per symbol (e.g., bit). Similar expressions can be derived toaccommodate other proposed forms of modulation.

An alternative form of time-shift modulation can be described asOne-of-Many Position Modulation (OMPM). The OMPM approach, shown in FIG.4B, involves shifting a pulse to one of N possible modulation positionsabout a nominal coded (or uncoded) time position in response to aninformation signal, where N represents the number of possible states.For example, if N were four (4), two data bits of information could beconveyed. For further details regarding OMPM, see “Apparatus, System andMethod for One-of-Many Position Modulation in an Impulse RadioCommunication System,” U.S. patent application Ser. No. 09/875,290,filed Jun. 7, 2000, assigned to the assignee of the present invention,and incorporated herein by reference.

An impulse radio communications system can employ flip modulationtechniques to convey information. The simplest flip modulation techniqueinvolves transmission of a pulse or an inverted (or flipped) pulse torepresent a data bit of information, as depicted in FIG. 4C. Flipmodulation techniques may also be combined with time-shift modulationtechniques to create two, four, or more different data states. One suchflip with shift modulation technique is referred to as Quadrature FlipTime Modulation (QFTM). The QFTM approach is illustrated in FIG. 4D.Flip modulation techniques are further described in patent applicationtitled “Apparatus, System and Method for Flip Modulation in an ImpulseRadio Communication System,” application Ser. No. 09/537,692, filed Mar.29, 2000, assigned to the assignee of the present invention, andincorporated herein by reference.

Vector modulation techniques may also be used to convey information.Vector modulation includes the steps of generating and transmitting aseries of time-modulated pulses, each pulse delayed by one of at leastfour pre-determined time delay periods and representative of at leasttwo data bits of information, and receiving and demodulating the seriesof time-modulated pulses to estimate the data bits associated with eachpulse. Vector modulation is shown in FIG. 4E. Vector modulationtechniques are further described in patent application titled “VectorModulation System and Method for Wideband Impulse Radio Communications,”application Ser. No. 09/169,765, filed Dec. 9, 1999, now abandoned,assigned to the assignee of the present invention, and incorporatedherein by reference.

Reception and Demodulation

Impulse radio systems operating within close proximity to each other maycause mutual interference. While coding minimizes mutual interference,the probability of pulse collisions increases as the number ofcoexisting impulse radio systems rises. Additionally, various othersignals may be present that cause interference. Impulse radios canoperate in the presence of mutual interference and other interferingsignals, in part because they do not depend on receiving everytransmitted pulse. Impulse radio receivers perform a correlating,synchronous receiving function (at the RF level) that uses statisticalsampling and combining, or integration, of many pulses to recovertransmitted information. Typically, 1 to 1000 or more pulses areintegrated to yield a single data bit thus diminishing the impact ofindividual pulse collisions, where the number of pulses that must beintegrated to successfully recover transmitted information depends on anumber of variables including pulse rate, bit rate, range andinterference levels.

Interference Resistance

Besides providing channelization and energy smoothing, coding makesimpulse radios highly resistant to interference by enablingdiscrimination between intended impulse transmissions and interferingtransmissions. This property is desirable since impulse radio systemsmust share the energy spectrum with conventional radio systems and withother impulse radio systems. FIG. 5A illustrates the result of a narrowband sinusoidal interference signal 502 overlaying an impulse radiosignal 504. At the impulse radio receiver, the input to the crosscorrelation would include the narrow band signal 502 and the receivedultrawide-band impulse radio signal 504. The input is sampled by thecross correlator using a template signal 506 positioned in accordancewith a code. Without coding, the cross correlation would sample theinterfering signal 502 with such regularity that the interfering signalscould cause interference to the impulse radio receiver. However, whenthe transmitted impulse signal is coded and the impulse radio receivertemplate signal 506 is synchronized using the identical code, thereceiver samples the interfering signals non-uniformly. The samples fromthe interfering signal add incoherently, increasing roughly according tothe square root of the number of samples integrated. The impulse radiosignal samples, however, add coherently, increasing directly accordingto the number of samples integrated. Thus, integrating over many pulsesovercomes the impact of interference.

Processing Gain

Impulse radio systems have exceptional processing gain due to their widespreading bandwidth. For typical spread spectrum systems, the definitionof processing gain, which quantifies the decrease in channelinterference when wide-band communications are used, is the ratio of thebandwidth of the channel to the bit rate of the information signal. Forexample, a direct sequence spread spectrum system with a 10 KHzinformation bandwidth and a 10 MHz channel bandwidth yields a processinggain of 1000, or 30 dB. However, far greater processing gains areachieved by impulse radio systems, where the same 10 KHz informationbandwidth is spread across a much greater 2 GHz channel bandwidth,resulting in a theoretical processing gain of 200,000, or 53 dB.

Capacity

It can be shown theoretically, using signal-to-noise arguments, thatthousands of simultaneous channels are available to an impulse radiosystem as a result of its exceptional processing gain.

The average output signal-to-noise ratio of the impulse radio may becalculated for randomly selected time-hopping codes as a function of thenumber of active users, N_(u), as:${{SNR}_{out}\left( N_{u} \right)} = \frac{\left( {N_{s}A_{1}m_{p}} \right)^{2}}{\sigma_{rec}^{2} + {N_{s}\sigma_{a}^{2}{\sum\limits_{k = 2}^{N_{u}}\quad A_{k}^{2}}}}$

where N_(s) is the number of pulses integrated per bit of information,A_(k) models the attenuation of transmitter k's signal over thepropagation path to the receiver, and σ_(rec) ² is the variance of thereceiver noise component at the pulse train integrator output. Themonocycle waveform-dependent parameters m_(p) and σ_(a) ² are given by$\begin{matrix}\begin{matrix}{m_{p} = {\int_{- \infty}^{\infty}{{{\omega (t)}\left\lbrack {{\omega (t)} - {\omega \left( {t - \delta} \right)}} \right\rbrack}\quad {t}}}} \\{and}\end{matrix} \\{{\sigma_{a}^{2} = {T_{f}^{- 1}{\int_{- \infty}^{\infty}{\left\lbrack {\int_{- \infty}^{\infty}{{\omega \left( {t - s} \right)}{\upsilon (t)}\quad {t}}} \right\rbrack^{2}\quad {s}}}}},}\end{matrix}$

where ω(t) is the monocycle waveform, u(t)=ω(t)−(t−δ) is the templatesignal waveform, δ is the time shift between the monocycle waveform andthe template signal waveform, T_(f) is the pulse repetition time, and sis signal.

Multipath and Propagation

One of the advantages of impulse radio is its resistance to multipathfading effects. Conventional narrow band systems are subject tomultipath through the Rayleigh fading process, where the signals frommany delayed reflections combine at the receiver antenna according totheir seemingly random relative phases resulting in possible summationor possible cancellation, depending on the specific propagation to agiven location. Multipath fading effects are most adverse where a directpath signal is weak relative to multipath signals, which represents themajority of the potential coverage area of a radio system. In a mobilesystem, received signal strength fluctuates due to the changing mix ofmultipath signals that vary as its position varies relative to fixedtransmitters, mobile transmitters and signal-reflecting surfaces in theenvironment.

Impulse radios, however, can be substantially resistant to multipatheffects. Impulses arriving from delayed multipath reflections typicallyarrive outside of the correlation time and, thus, may be ignored. Thisprocess is described in detail with reference to FIGS. 5B and 5C. FIG.5B illustrates a typical multipath situation, such as in a building,where there are many reflectors 504B, 505B. In this figure, atransmitter 506B transmits a signal that propagates along three paths,the direct path 501B, path 1 502B, and path 2 503B, to a receiver 508B,where the multiple reflected signals are combined at the antenna. Thedirect path 501B, representing the straight-line distance between thetransmitter and receiver, is the shortest. Path 1 502B represents amultipath reflection with a distance very close to that of the directpath. Path 2 503B represents a multipath reflection with a much longerdistance. Also shown are elliptical (or, in space, ellipsoidal) tracesthat represent other possible locations for reflectors that wouldproduce paths having the same distance and thus the same time delay.

FIG. 5C illustrates the received composite pulse waveform resulting fromthe three propagation paths 501B, 502B, and 503B shown in FIG. 5B. Inthis figure, the direct path signal 501B is shown as the first pulsesignal received. The path 1 and path 2 signals 502B, 503B comprise theremaining multipath signals, or multipath response, as illustrated. Thedirect path signal is the reference signal and represents the shortestpropagation time. The path 1 signal is delayed slightly and overlaps andenhances the signal strength at this delay value. The path 2 signal isdelayed sufficiently that the waveform is completely separated from thedirect path signal. Note that the reflected waves are reversed inpolarity. If the correlator template signal is positioned such that itwill sample the direct path signal, the path 2 signal will not besampled and thus will produce no response. However, it can be seen thatthe path 1 signal has an effect on the reception of the direct pathsignal since a portion of it would also be sampled by the templatesignal. Generally, multipath signals delayed less than one quarter wave(one quarter wave is about 1.5 inches, or 3.5 cm at 2 GHz centerfrequency) may attenuate the direct path signal. This region isequivalent to the first Fresnel zone in narrow band systems. Impulseradio, however, has no further nulls in the higher Fresnel zones. Thisability to avoid the highly variable attenuation from multipath givesimpulse radio significant performance advantages.

FIGS. 5D, 5E, and 5F represent the received signal from a TM-UWBtransmitter in three different multipath environments. These figures areapproximations of typical signal plots. FIG. 5D illustrates the receivedsignal in a very low multipath environment. This may occur in a buildingwhere the receiver antenna is in the middle of a room and is arelatively short, distance, for example, one meter, from thetransmitter. This may also represent signals received from a largerdistance, such as 100 meters, in an open field where there are noobjects to produce reflections. In this situation, the predominant pulseis the first received pulse and the multipath reflections are too weakto be significant. FIG. 5E illustrates an intermediate multipathenvironment. This approximates the response from one room to the next ina building. The amplitude of the direct path signal is less than in FIG.5D and several reflected signals are of significant amplitude. FIG. 5Fapproximates the response in a severe multipath environment such aspropagation through many rooms, from corner to corner in a building,within a metal cargo hold of a ship, within a metal truck trailer, orwithin an intermodal shipping container. In this scenario, the main pathsignal is weaker than in FIG. 5E. In this situation, the direct pathsignal power is small relative to the total signal power from thereflections.

An impulse radio receiver can receive the signal and demodulate theinformation using either the direct path signal or any multipath signalpeak having sufficient signal-to-noise ratio. Thus, the impulse radioreceiver can select the strongest response from among the many arrivingsignals. In order for the multipath signals to cancel and produce a nullat a given location, dozens of reflections would have to be cancelledsimultaneously and precisely while blocking the direct path, which is ahighly unlikely scenario. This time separation of mulitipath signalstogether with time resolution and selection by the receiver permit atype of time diversity that virtually eliminates cancellation of thesignal. In a multiple correlator rake receiver, performance is furtherimproved by collecting the signal power from multiple signal peaks foradditional signal-to-noise performance.

Where the system of FIG. 5B is a narrow band system and the delays aresmall relative to the data bit time, the received signal is a sum of alarge number of sine waves of random amplitude and phase. In theidealized limit, the resulting envelope amplitude has been shown tofollow a Rayleigh probability distribution as follows:${p(r)} = {\frac{r}{\sigma^{2}}{\exp \left( \frac{- r^{2}}{2\sigma^{2}} \right)}}$

where r is the envelope amplitude of the combined multipath signals, andσ(2)^(1/2) is the RMS power of the combined multipath signals. TheRayleigh distribution curve in FIG. 5G shows that 10% of the time, thesignal is more than 10 dB attenuated. This suggests that 10 dB fademargin is needed to provide 90% link availability. Values of fade marginfrom 10 to 40 dB have been suggested for various narrow band systems,depending on the required reliability. This characteristic has been thesubject of much research and can be partially improved by suchtechniques as antenna and frequency diversity, but these techniquesresult in additional complexity and cost.

In a high multipath environment such as inside homes, offices,warehouses, automobiles, trailers, shipping containers, or outside in anurban canyon or other situations where the propagation is such that thereceived signal is primarily scattered energy, impulse radio systems canavoid the Rayleigh fading mechanism that limits performance of narrowband systems, as illustrated in FIGS. 5H and 5I. FIG. 5H depicts animpulse radio system in a high multipath environment 500H consisting ofa transmitter 506H and a receiver 508H. A transmitted signal follows adirect path 501H and reflects off reflectors 503H via multiple paths502H. FIG. 5I illustrates the combined signal received by the receiver508H over time with the vertical axis being signal strength in volts andthe horizontal axis representing time in nanoseconds. The direct path501H results in the direct path signal 502I while the multiple paths502H result in multipath signals 504I. In the same manner describedearlier for FIGS. 5B and 5C, the direct path signal 502I is sampled,while the multipath signals 504I are not, resulting in Rayleigh fadingavoidance.

Distance Measurement and Positioning

Impulse systems can measure distances to relatively fine resolutionbecause of the absence of ambiguous cycles in the received waveform.Narrow band systems, on the other hand, are limited to the modulationenvelope and cannot easily distinguish precisely which RF cycle isassociated with each data bit because the cycle-to-cycle amplitudedifferences are so small they are masked by link or system noise. Sincean impulse radio waveform has no multi-cycle ambiguity, it is possibleto determine waveform position to less than a wavelength, potentiallydown to the noise floor of the system. This time position measurementcan be used to measure propagation delay to determine link distance to ahigh degree of precision. For example, 30 ps of time transfer resolutioncorresponds to approximately centimeter distance resolution. See, forexample, U.S. Pat. No. 6,133,876, issued Oct. 17, 2000, titled “Systemand Method for Position Determination by Impulse Radio,” and U.S. Pat.No. 6,111,536, issued Aug. 29, 2000, titled “System and Method forDistance Measurement by Inphase and Quadrature Signals in a RadioSystem,” both of which are incorporated herein by reference.

In addition to the methods articulated above, impulse radio technologyalong with Time Division Multiple Access algorithms and Time Domainpacket radios can achieve geo-positioning capabilities in a radionetwork. This geo-positioning method is described in co-owned,co-pending U.S. Pat. No. 6,300,903 entitled “System and Method forPerson or Object Position Location Utilizing Impulse Radio,” which isincorporated herein by reference.

Power Control

Power control systems comprise a first transceiver that transmits animpulse radio signal to a second transceiver. A power control update iscalculated according to a performance measurement of the signal receivedat the second transceiver. The transmitter power of either transceiver,depending on the particular setup, is adjusted according to the powercontrol update. Various performance measurements are employed tocalculate a power control update, including bit error rate,signal-to-noise ratio, and received signal strength, used alone or incombination. Interference is thereby reduced, which may improveperformance where multiple impulse radios are operating in closeproximity and their transmissions interfere with one another. Reducingthe transmitter power of each radio to a level that producessatisfactory reception increases the total number of radios that canoperate in an area without saturation. Reducing transmitter power alsoincreases transceiver efficiency.

For greater elaboration of impulse radio power control, see patentapplication titled “System and Method for Impulse Radio Power Control,”application Ser. No. 09/332,501, filed Jun. 14, 1999, assigned to theassignee of the present invention, and incorporated herein by reference.

Mitigating Effects of Interference

A method for mitigating interference in impulse radio systems comprisesthe steps of conveying the message in packets, repeating conveyance ofselected packets to make up a repeat package, and conveying the repeatpackage a plurality of times at a repeat period greater than twice theperiod of occurrence of the interference. The communication may convey amessage from a proximate transmitter to a distant receiver, and receivea message by a proximate receiver from a distal transmitter. In such asystem, the method comprises the steps of providing interferenceindications by the distal receiver to the proximate transmitter, usingthe interference indications to determine predicted noise periods, andoperating the proximate transmitter to convey the message according toat least one of the following: (1) avoiding conveying the message duringnoise periods, (2) conveying the message at a higher power during noiseperiods, (3) increasing error detection coding in the message duringnoise periods, (4) re-transmitting the message following noise periods,(5) avoiding conveying the message when interference is greater than afirst strength, (6) conveying the message at a higher power when theinterference is greater than a second strength, (7) increasing errordetection coding in the message when the interference is greater than athird strength, and (8) re-transmitting a portion of the message afterinterference has subsided to less than a predetermined strength.

For greater elaboration of mitigating interference in impulse radiosystems, see the patent application titled “Method for MitigatingEffects of Interference in Impulse Radio Communication,” applicationSer. No. 09/587,033, filed Jun. 2, 2000, assigned to the assignee of thepresent invention, and incorporated herein by reference.

Moderating Interference in Equipment Control Applications

Yet another improvement to impulse radio includes moderatinginterference with impulse radio wireless control of an appliance. Thecontrol is affected by a controller remote from the appliance whichtransmits impulse radio digital control signals to the appliance. Thecontrol signals have a transmission power and a data rate. The methodcomprises the steps of establishing a maximum acceptable noise value fora parameter relating to interfering signals and a frequency range formeasuring the interfering signals, measuring the parameter for theinterference signals within the frequency range, and effecting analteration of transmission of the control signals when the parameterexceeds the maximum acceptable noise value.

For greater elaboration of moderating interference while effectingimpulse radio wireless control of equipment, see patent applicationtitled “Method and Apparatus for Moderating Interference While EffectingImpulse Radio Wireless Control of Equipment,” application Ser. No.09/586,163, filed Jun. 2, 1999, now U.S. Pat. No. 6,571,089, andassigned to the assignee of the present invention, and incorporatedherein by reference.

Exemplary Transceiver Implementation

Transmitter

An exemplary embodiment of an impulse radio transmitter 602 of animpulse radio communication system having an optional subcarrier channelwill now be described with reference to FIG. 6.

The transmitter 602 comprises a time base 604 that generates a periodictiming signal 606. The time base 604 typically comprises a voltagecontrolled oscillator (VCO), or the like, having a high timing accuracyand low jitter, on the order of picoseconds (ps). The control voltage toadjust the VCO center frequency is set at calibration to the desiredcenter frequency used to define the transmitter's nominal pulserepetition rate. The periodic timing signal 606 is supplied to aprecision timing generator 608.

The precision timing generator 608 supplies synchronizing signals 610 tothe code source 612 and utilizes the code source output 614, togetherwith an optional, internally generated subcarrier signal, and aninformation signal 616, to generate a modulated, coded timing signal618.

An information source 620 supplies the information signal 616 to theprecision timing generator 608. The information signal 616 can be anytype of intelligence, including digital bits representing voice, data,imagery, or the like, analog signals, or complex signals.

A pulse generator 622 uses the modulated, coded timing signal 618 as atrigger signal to generate output pulses. The output pulses are providedto a transmit antenna 624 via a transmission line 626 coupled thereto.The output pulses are converted into propagating electromagnetic pulsesby the transmit antenna 624. The electromagnetic pulses are called theemitted signal, and propagate to an impulse radio receiver 702, such asshown in FIG. 7, through a propagation medium. In a preferredembodiment, the emitted signal is wide-band or ultrawide-band,approaching a monocycle pulse as in FIG. 1B. However, the emitted signalmay be spectrally modified by filtering of the pulses, which may causethem to have more zero crossings (more cycles) in the time domain,requiring the radio receiver to use a similar waveform as the templatesignal for efficient conversion.

Receiver

An exemplary embodiment of an impulse radio receiver (hereinafter calledthe receiver) for the impulse radio communication system is nowdescribed with reference to FIG. 7.

The receiver 702 comprises a receive antenna 704 for receiving apropagated impulse radio signal 706. A received signal 708 is input to across correlator or sampler 710, via a receiver transmission line,coupled to the receive antenna 704. The cross correlation 710 produces abaseband output 712.

The receiver 702 also includes a precision timing generator 714, whichreceives a periodic timing signal 716 from a receiver time base 718.This time base 718 may be adjustable and controllable in time,frequency, or phase, as required by the lock loop in order to lock onthe received signal 708. The precision timing generator 714 providessynchronizing signals 720 to the code source 722 and receives a codecontrol signal 724 from the code source 722. The precision timinggenerator 714 utilizes the periodic timing signal 716 and code controlsignal 724 to produce a coded timing signal 726. The template generator728 is triggered by this coded timing signal 726 and produces a train oftemplate signal pulses 730 ideally having waveforms substantiallyequivalent to each pulse of the received signal 708. The code forreceiving a given signal is the same code utilized by the originatingtransmitter to generate the propagated signal. Thus, the timing of thetemplate pulse train matches the timing of the received signal pulsetrain, allowing the received signal 708 to be synchronously sampled inthe correlator 710. The correlator 710 preferably comprises a multiplierfollowed by a short term integrator to sum the multiplier product overthe pulse interval.

The output of the correlator 710 is coupled to a subcarrier demodulator732, which demodulates the subcarrier information signal from theoptional subcarrier. The purpose of the optional subcarrier process,when used, is to move the information signal away from DC (zerofrequency) to improve immunity to low frequency noise and offsets. Theoutput of the subcarrier demodulator is then filtered or integrated inthe pulse summation stage 734. A digital system embodiment is shown inFIG. 7. In this digital system, a sample and hold 736 samples the output735 of the pulse summation stage 734 synchronously with the completionof the summation of a digital bit or symbol. The output of sample andhold 736 is then compared with a nominal zero (or reference) signaloutput in a detector stage 738 to provide an output signal 739representing the digital state of the output voltage of sample and hold736.

The baseband signal 712 is also input to a lowpass filter 742 (alsoreferred to as lock loop filter 742). A control loop comprising thelowpass filter 742, time base 718, precision timing generator 714,template generator 728, and correlator 710 is used to generate an errorsignal 744. The error signal 744 provides adjustments to the adjustabletime base 718 to position in time the periodic timing signal 726 inrelation to the position of the received signal 708.

In a transceiver embodiment, substantial economy can be achieved bysharing part or all of several of the functions of the transmitter 602and receiver 702. Some of these include the time base 718, precisiontiming generator 714, code source 722, antenna 704, and the like.

FIGS. 8A-8C illustrate the cross correlation process and the correlationfunction. FIG. 8A shows the waveform of a template signal. FIG. 8B showsthe waveform of a received impulse radio signal at a set of severalpossible time offsets. FIG. 8C represents the output of the crosscorrelator for each of the time offsets of FIG. 8B. For any given pulsereceived, there is a corresponding point that is applicable on thisgraph. This is the point corresponding to the time offset of thetemplate signal used to receive that pulse. Further examples and detailsof precision timing can be found described in U.S. Pat. Nos. 5,677,927and 6,304,623 both of which are incorporated herein by reference.

Because of the unique nature of impulse radio receivers, severalmodifications have been recently made to enhance system capabilities.Modifications include the utilization of multiple correlators to measurethe impulse response of a channel to the maximum communications range ofthe system and to capture information on data symbol statistics.Further, multiple correlators enable rake pulse correlation techniques,more efficient acquisition and tracking implementations, variousmodulation schemes, and collection of time-calibrated pictures ofreceived waveforms. For greater elaboration of multiple correlatortechniques, see patent application titled “System and Method of usingMultiple Correlator Receivers in an Impulse Radio System”, applicationSer. No. 09/537,264, filed Mar. 29, 2000, assigned to the assignee ofthe present invention, and incorporated herein by reference.

Methods to improve the speed at which a receiver can acquire and lockonto an incoming impulse radio signal have been developed. In oneapproach, a receiver includes an adjustable time base to output asliding periodic timing signal having an adjustable repetition rate anda decode timing modulator to output a decode signal in response to theperiodic timing signal. The impulse radio signal is cross-correlatedwith the decode signal to output a baseband signal. The receiverintegrates T samples of the baseband signal and a threshold detectoruses the integration results to detect channel coincidence. A receivercontroller stops sliding the time base when channel coincidence isdetected. A counter and extra count logic, coupled to the controller,are configured to increment or decrement the address counter by one ormore extra counts after each T pulses is reached in order to shift thecode modulo for proper phase alignment of the periodic timing signal andthe received impulse radio signal. This method is described in moredetail in U.S. Pat. No. 5,832,035 to Fullerton, incorporated herein byreference.

In another approach, a receiver obtains a template pulse train and areceived impulse radio signal. The receiver compares the template pulsetrain and the received impulse radio signal. The system performs athreshold check on the comparison result. If the comparison resultpasses the threshold check, the system locks on the received impulseradio signal. The system may also perform a quick check, asynchronization check, and/or a command check of the impulse radiosignal. For greater elaboration of this approach, see the patentapplication titled “Method and System for Fast Acquisition of UltraWideband Signals,” application Ser. No. 09/538,292, filed Mar. 29, 2000,now U.S. Pat. 6,556,621, assigned to the assignee of the presentinvention, and incorporated herein by reference.

A receiver has been developed that includes a baseband signal converterdevice and combines multiple converter circuits and an RF amplifier in asingle integrated circuit package. For greater elaboration of thisreceiver, see U.S. Pat. No. 6,421,389 entitled “Baseband SignalConverter for a Wideband Impulse Radio Receiver,” which is assigned tothe assignee of the present invention, and incorporated herein byreference.

UWB Intrusion Detection System and Method

Referring to FIGS. 9-22, there are disclosed three embodiments ofexemplary intrusion detection systems 1100, 1100′ and 1100″ andpreferred methods 1600, 1600′ and 1600″ in accordance with the presentinvention.

Although the present invention is described as using impulse radiotechnology, it should be understood that the present invention can beused with any type of ultra wideband technology, but is especiallysuited for use with time-modulated ultra wideband technology.Accordingly, the exemplary intrusion detection systems 1100, 1100′ and1100″ and preferred methods 1600, 1600′ and 1600″ should not beconstrued in a limited manner.

Generally, in the first embodiment, the intrusion detection system 1100and method 1600 utilize impulse radio technology to detect when anintruder 1102 has entered a protection zone 1104 (see FIGS. 11 and14-16). In the second embodiment, the intrusion detection system 1100′and method 1600′ can utilize impulse radio technology to determine alocation of the intruder 1102′ within the protection zone 1104′ and alsotrack the movement of the intruder 1102′ within the protection zone1104′ (see FIGS. 12 and 17-19). In the third embodiment, the intrusiondetection system 1100″ and method 1600″ utilize impulse radio technologyto create a specially shaped protection zone 1104″ before trying todetect when and where the intruder 1102″ has penetrated and moved withinthe protection zone 1104″ (see FIGS. 13 and 20-21). Each of the threeembodiments are briefly described below with respect to FIGS. 9-13 priorto describing each embodiment in greater detail with respect to FIGS.14-21.

The present invention as described uses one or more ultra-wideband (UWB)scanning receivers 900 and a UWB transmitter 1000 as bistatic radar(s)to enable short-range target detection and positioning. The intrusiondetection system described provides a robust, cost effective way fordetecting the introduction of foreign objects including intruders ofappreciable radar cross section (RCS) into a constrained and stationaryenvironment such as a protection zone. Some of the benefits ofimplementing UWB technology for this application is that it enables theintrusion detection system to offer excellent time (distance)resolution, clutter rejection, and also enables the intrusion detectionsystem to extend the range of coverage through barriers. In addition,due to the low transmit power, the intrusion detection system isresistant to both detection and jamming.

UWB Scanning Receiver and UWB Transmitter

FIGS. 9-10, illustrate exemplary block diagrams of the UWB scanningreceiver 900 and its companion the UWB transmitter 1000. Time DomainCorporation has developed the UWB scanning receiver 900 that implementstime-modulated ultra-wideband (TM-UWB) technology and utilizes shortGaussian monocycle pulses at relatively high pulse repetitionfrequencies (PRF). The pulse durations are less than 1 ns with a PRFexceeding 1 MHz. The interval between pulses is not fixed but is timecoded using sequences of psuedo-random numbers. See, Withington,Reinhardt, and Stanley, “Preliminary Results of an Ultra-Wideband(Impulse) Scanning Receiver”, Paper S38P3, Milcom 1999, Atlantic City,N.J., November 1999 which is incorporated herein.

In the implementation shown, the UWB transmitter 1000 emits a stream of500 ps TM-UWB coded pulses at a PRF of 10 MHz using an independenttiming system 1002 and 1004. The UWB scanning receiver 900 includes twocorrelators 906 and 908 each of which are controlled by an independenttiming system 902, 904 and 910. Time Domain has also developed theseprecision, low noise synchronous programmable time delay integratedcircuits 902, 904, 910, 1002 and 1004. See, L. Larson, et al., “A SI/GeHBT Timing Generator IC for High Bandwidth Impulse Radio Applications,”Custom Integrated Circuits Conference 1999, San Diego, Calif., May 1999which is incorporated herein.

The tracking correlator 906 within the UWB receiver 900 synchronizeswith and is able to track the received pulse train, providing coherenttransmission. Any offset between the receiver's internal coded waveformand the received coded waveform is detected as an error voltage in thecorrelator's lock loop. A frequency offset is synthesized to offset thepseudo-random time hopping word, thus ensuring the receiver's clock 910is within 20 ps RMS of the transmitter's clock 1004. Once the trackingcorrelator 906 is locked to the received signal, the scanning correlator908 can sample the received waveform at precise time delays generating acomplete picture of the received signal. This picture is representativeof the actual distortion of the transmitted Gaussian waveform afterbeing filtered by the environment.

It should be noted that the scanning correlator 908 can dwell at a timeposition for a user-specified number of integrated pulses to mitigatethe effects of noise and other non-coherent interference. Timeresolution steps as small as 3.052 ps can be specified but a typicaltime sample resolution is approximately 30 ps.

Implementing the UWB scanning receiver 900 in a multipath environmentresults in a scanning receiver output that represents a psuedo-channelimpulse of the propagation channel. The multipath channel ischaracterized by the line of sight (LOS) signal (if one exists) alongwith delayed, attenuated copies of the transmitted signal correspondingto reflections off of objects including intruders in the environment.The multipath structure of the propagation channel is unique to theplacement of objects in the protection zone as well as the placement ofthe transmit and receive antennas 1006 and 911, respectively. Assumingthat the propagation environment is stationary (i.e. all reflectivesurfaces and antennas are fixed and no intruders are present),successive multipath scans taken by the scanning receiver 900 areidentical. This can be verified to ensure stationarity via a simplesubtraction and digital filtering of the successive scan waveforms. Asdescribed in greater detail below, the scan waveforms that are made whenan intruder is not present are later compared to scan waveforms that aremade when an intruder is present which enables the detection of theintruder. Further examples and details about the basic components withinthe UWB scanning receiver 900 and the UWB transmitter 1000 can be foundin the commonly owned U.S. patent application Ser. No. 09/537,264, filedMar. 29, 2000, entitled “System and Method of using Multiple CorrelatorReceivers in an Impulse Radio System” which is incorporated herein byreference.

Intruder Detection (First Embodiment)

Referring to FIG. 11, there is illustrated a diagram of the basiccomponents of the first embodiment of the intrusion detection system1100. Basically, the intrusion detection system 1000 includes the UWBscanning receiver 900 and the UWB transmitter 1000 which togetherfunction as a bistatic radar to facilitate target detection. Theintroduction of any new object such as an intruder 1102 having anappreciable RCS into the environment alters the multipath structure ofthe protection zone 1104 and distorts the received scan waveform. Thepresence of the intruder 1102 is now detectable in the subtraction ofsuccessive scans; any significant change in a portion of this differencereveals the range of the intruder 1102 with respect to the placement ofthe UWB scanning receiver 900. Knowing the distance from the UWBtransmitter 1000 to the UWB scanning receiver 900 and knowing therelative time delay of the target response in the scanned waveform, theposition of the intruder 1102 is known to lie somewhere on an ellipsewhose foci are the UWB transmitter 1000 and the UWB receiver 900. Asillustrated, the intruder 1102 is located in one of two possiblelocations.

Empirical data has shown that for successive scans of an environment inwhich no intruder 1102 is present, limitations of the UWB scanningreceiver 900 such as timer drift and small amplitude variations preventsuccessive scans from having perfect subtraction. This creates a certainclutter threshold in the subtracted waveform. The limitations of the UWBscanning receiver 900 require that the intruder 1102 introduced to theenvironment must reflect a return to the receive antenna 911 that isdistinguishable from clutter. Effective filters and relevantthresholding techniques are used to combat this drift. Again, moredetails about the first embodiment of the intrusion detection system1100 and various scanned waveforms are described below with respect toFIGS. 14-16.

Intruder Positioning (Second Embodiment)

Referring to FIG. 12, there is illustrated a block diagram of the basiccomponents of the second embodiment of the intrusion detection system1100′. The intrusion detection system 1100′ extends the functionality ofthe intrusion detection system 1100 by implementing multiple UWBscanning receivers 900′ (three shown) which can interact with the UWBtransmitter 1000′ to triangulate the current position of the intruder1102′. Coordinating the measured target ranges of multiple UWB scanningreceivers 900′ can allow for precise positioning of the intruder 1102′via an intersection of the ranging ellipses of known distance of theintruder 1102′ from each transmitter-receiver pair. This triangulationof the intruder 1102′ is graphically shown in FIG. 12.

Empirical data has shown that the UWB scanning receivers 900′ havesub-nanosecond time resolution, corresponding to ranging accuracy ofless than 1 foot. The ranging ellipses of each individualtransmitter/receiver are solved to determine the position of intruder1102′ via a numerical algorithm such as Newton-Raphson method or someother techniques.

Design the Shape of the Protection Zone (Third Embodiment)

The main difference between the second embodiment of the intrusiondetection system 1100′ and the third embodiment of the intrusiondetection system 1100″ is that the third embodiment enables the creationof an unusually shaped protection zone 1104″ within the region that thetarget ellipses could converge due to an intrusion instead of using theelliptical zones shown in FIG. 12. Prior to arming the intrusiondetection system 1100″, the system can be put into a “learning mode”.During the “learning mode”, a person 1300″ would traverse the perimeterof the protection zone 1104″ to be protected and the intrusion detectionsystem 1100″ would track the person 1300″ and build a two and possiblythree-dimensional representation of the shape of the protection zone1104″ (see FIG. 13).

Detailed Description of First Embodiment

Referring to FIG. 14, there is a diagram illustrating the firstembodiment of the intrusion detection system 1100 in accordance with thepresent invention. The intrusion detection system 1100 includes atransmitting impulse radio unit 1000 (described above as the UWBtransmitter 1000) and a receiving impulse radio unit 900 (describedabove as the UWB scanning receiver 900). The transmitting impulse radiounit 1000 transmits an impulse radio signal 1402 having a knownpseudorandom sequence of pulses that look like a series of Gaussianwaveforms (see FIG. 1).

Initially, the impulse radio signal 1402 is transmitted within andthrough a protection zone 1104 that does not have an intruder 1102. Thereceiving impulse radio unit 900 receives the impulse radio signal 1402and generates a first waveform 1502 (an exemplary first waveform isshown in FIG. 15a). The first waveform 1502 is a time domainrepresentation of the actual distortion of the transmitted Gaussianwaveform after being filtered by the environment around the transmittingimpulse radio unit 1000 and the receiving impulse radio unit 900. Inother words, the first waveform 1502 corresponds to the received impulseshape of the impulse radio signal 1402 that is received by the receivingimpulse radio unit 900 when there is no intruder 1102 located in theprotection zone 1104.

After the generation of the first waveform 1502, the receiving impulseradio unit 900 receives at a subsequent time “t_(s)” the impulse radiosignal 1402 having a known pseudorandom sequence of pulses that aresimilar to the pulses initially transmitted by the transmitting impulseradio unit 1000 during the generation of the first waveform 1502.However at this time, the impulse radio signal 1402 is transmittedwithin and through a protection zone 1104 that does have an intruder1102. In particular, the receiving impulse radio unit 900 receives theimpulse radio signal 1402 that passed over a direct path 1404 betweenthe transmitting impulse radio unit 1000 and the receiving impulse radiounit 900. The presence of the intruder 1102 causes the receiving impulseradio unit 900 to also receive the impulse radio signal 1402 that passedover an indirect path 1406 between the transmitting impulse radio unit1000 and the receiving impulse radio unit 900. The receiving impulseradio unit 900 receives both of these impulse radio signals 1402 inaddition to other reflected impulse radio signals 1402 (not shown) overtime and generates a second waveform 1504 (an exemplary second waveform1504 is shown in FIG. 15b). The second waveform 1504 is a time domainrepresentation of the actual distortion of the transmitted Gaussianwaveforms after being bounced of the intruder 1102 and filtered by theenvironment around the transmitting impulse radio unit 1000 and thereceiving impulse radio unit 900. In other words, the second waveform1504 corresponds to the received impulse shapes of the impulse radiosignals 1402 that are received by the receiving impulse radio unit 900when the intruder 1102 is located in the protection zone 1104.

The receiving impulse radio unit 900 includes a processor 1408 thatcompares the first waveform 1502 and the second waveform 1504 todetermine whether there is a change between the first waveform 1502 andthe second waveform 1504 caused by an intruder 1102 entering theprotection zone 1104. To illustrate this change between waveformsreference is made to FIGS. 15a and 15 b, where there are illustrated twoexemplary waveforms 1502 and 1504 that could be generated by thereceiving impulse radio unit 900. The first waveform 1502 has an initialwavefront 1503 representative of the first received impulse radio pulsesof the impulse radio signal 1402. Likewise, the second waveform 1504generated after the first waveform 1502 has an initial wavefront 1506representative of the first received impulse radio pulse of thesubsequently received impulse radio signal 1402. In addition, the secondwaveform 1504 has a multipath reflection part 1508 caused by theintruder 1102 that was absent in the first waveform 1502 but present inthe second waveform 1504. This multipath reflection part 1508 is causedby the reception of the impulse radio signal 1402 that bounced off theintruder 1102 and passed over the indirect path 1406 between thetransmitting impulse radio unit 1000 and the receiving impulse radiounit 900. The distance “d” between the intruder 1102 and the receivingimpulse radio unit 900 can be calculated knowing the elapsed time “t”between the initial wavefront 1506 and the multipath reflection part1508 of the second waveform 1504. Once the distance “d” is calculated,the intruder 1102 could be in one of many places indicated by theellipse shown in FIG. 14 (shown are two possible positions of theintruder 1102).

It should be understood that there may be many items (e.g., walls,trees, furniture . . . ) within the protection zone 1104 that couldcause a multipath reflection part in the first and second waveforms 1502and 1504 but it is the difference between the two waveforms 1502 and1504 that indicates the presence of one or more intruders 1102.Moreover, it should be noted that the shape of the protection zone 1104in the first embodiment is basically arbitrary as compared to thespecially designed shape of the protection zone 1104″ in the thirdembodiment.

Referring to FIG. 16, there is a flowchart illustrating the basic stepsof a first embodiment of the preferred method 1600 of the presentinvention. Beginning at step 1602, the transmitting impulse radio unit1000 operates to transmit the impulse radio signal 1402. At this time,the impulse radio signal 1402 is made up of impulse radio pulses thatare transmitted within and through a protection zone 1104 that does nothave an intruder 1102. A more detailed discussion about the transmittingimpulse radio unit 1000 has been provided above with respect to FIG. 10.

At step 1604, the receiving impulse radio unit 900 operates to receivethe impulse radio signal 1402 and generate the first waveform 1502.Again, the receiving impulse radio unit 900 receives the impulse radiosignal 1402 and generates a first waveform 1502 (see FIG. 15a) that is atime domain representation of the actual distortion of the transmittedGaussian waveform after being filtered by the environment around thetransmitting impulse radio unit 1000 and the receiving impulse radiounit 900. In other words, the first waveform 1502 corresponds to thereceived impulse shape of the impulse radio signal 1402 that is receivedby the receiving impulse radio unit 900 when there is no intruder 1102located in the protection zone 1104. A more detailed discussion aboutthe receiving impulse radio unit 1000 has been provided above withrespect to FIG. 9.

At step 1606 and at a subsequent time with respect to steps 1602 and1604, the receiving impulse radio unit 900 operates to receive theimpulse radio signal 1402 and generate the second waveform 1504. In thepresent example, the second waveform 1504 (see FIG. 15b) illustrateswhat the impulse radio signals 1402 received by the receiving impulseradio unit 900 looks like in the time domain with an intruder 1102located in the protection zone 1104. In other words, the second waveform1504 corresponds to the received impulse shape of the impulse radiosignals 1402 that are received by the receiving impulse radio unit 900over the direct path 1404 and the indirect path 1406 when the intruder1102 is located in the protection zone 1104.

At step 1608, the processor 1408 within the receiving impulse radio unit900 operates to compare the first waveform 1502 and the second waveform1504 to determine whether there is a change between the first waveform1502 and the second waveform 1504 caused by an intruder 1102 enteringthe protection zone 1104. In the present example, there is a changebetween the first waveform 1502 and the second waveform 1504 because anintruder 1102 was not present when the first waveform 1502 was generatedbut the intruder 1102 was present when the second waveform 1504 wasgenerated by the receiving impulse radio unit 900 (see FIGS. 15a-15 b).This change is noticeable due to the presence of the multipathreflection part 1508 caused by the intruder 1102. Of course, thereceiving impulse radio unit 900 may generate many second waveforms inwhich there is no difference or very little difference with a firstwaveform because an intruder 1102 was not present. If an intruder 1102is not present in the protection zone 1104 then the method 1600 returnsto and repeats steps 1606 and 1608 until an intruder 1102 is determinedto be present in the protection zone 1104.

At step 1610, if the intruder 1102 is determined to be in the protectionzone 1104, the processor 1408 could then calculate the difference “d”between the direct path between the transmitter 1000 and receiver 900and the indirect path 1402 by knowing the elapsed time “t” between theinitial wavefront 1506 and the multipath reflection part 1508 of thesecond waveform 1504 (see FIG. 15b). For instance, the distance “d” canbe calculated to be 0.984 feet for each nanosecond in the elapsed time“t” between the initial wavefront 1506 and the multipath reflection part1508 of the second waveform 1504 (see FIG. 15b). In this embodiment, theintruder 1102 could be in one of many places indicated by the ellipseshown in FIG. 14 (shown are two possible positions of the intruder1102). Reference is made to the second embodiment of the intrusiondetection system 1100′ which can determine the real location of theintruder 1102.

At step 1612, the receiving impulse radio unit 900 sounds an alarmand/or informs remote security personnel when there is an intruder 1102present in the protection zone 1104. For extra security, the receivingimpulse radio unit 900 can use impulse radio technology to alert theremote security personnel.

Detailed Description of Second Embodiment

Referring to FIG. 17, there is a diagram illustrating a secondembodiment of the intrusion detection system 1100 in accordance with thepresent invention. The second embodiment of the intrusion detectionsystem 1000 is illustrated using prime referenced numbers. Basically,the intrusion detection system 1000′ is the same as the first embodimentexcept that at least three receiving impulse radio units 900 a′, 900 b′and 900 c′ are used to enable a current position of the intruder 1102′to be triangulated and determined within the protection zone 1104′. Eachof the three receiving impulse radio units 900 a′, 900 b′ and 900 c′operate in a similar manner as the receiving impulse radio unit 900 ofthe first embodiment.

The intrusion detection system 1100′ includes a transmitting impulseradio unit 1000′ and at least three receiving impulse radio units 900a′, 900 b′ and 900 c′. The transmitting impulse radio unit 1000′transmits an impulse radio signal 1402′ having a known pseudorandomsequence of pulses that look like a series of Gaussian waveforms (seeFIG. 1). Initially, the impulse radio signal 1402′ is transmitted withinand through a protection zone 1104′ that does not have an intruder1102′.

Each receiving impulse radio unit 900 a′, 900 b′ and 900 c′ respectivelyreceives the first impulse radio signal 1402′ and generates a firstwaveform 1502 a′, 1502 b′ and 1502 c′ (see FIG. 18a). The first waveform1502 a′, 1502 b′ and 1502 c′ is a time domain representation of theactual distortion of the transmitted Gaussian waveform after beingfiltered by the environment around the transmitting impulse radio unit1000′ and each receiving impulse radio unit 900 a′, 900 b′ and 900 c′.In other words, each first waveform 1502 a′, 1502 b′ and 1502 c′corresponds to the received impulse shape of the impulse radio signal1402′ that is received by the receiving impulse radio units 900 a′, 900b′ and 900 c′ when there is no intruder 1102′ located in the protectionzone 1104′.

After the generation of the first waveforms 1502 a′, 1502 b′ and 1502c′, each receiving impulse radio unit 900 a′, 900 b′ and 900 c′ receivesat a subsequent time “t_(s)” the impulse radio signal 1402′ having aknown pseudorandom sequence of pulses that are similar to the pulsesinitially transmitted by the transmitting impulse radio unit 1000′during the generation of the first waveforms 1502 a′, 1502 b′ and 1502c′. However at this time, the impulse radio signal 1402′ is transmittedwithin and through a protection zone 1104′ that does have an intruder1102′.

In particular, each receiving impulse radio unit 900 a′, 900 b′ and 900c′ respectively receives the impulse radio signal 1402′ that passed overa direct path 1404 a′, 1404 b′ and 1404 c′ between the transmittingimpulse radio unit 1000′ and the receiving impulse radio units 900 a′,900 b′ and 900 c′. The presence of the intruder 1102′ causes eachreceiving impulse radio unit 900 a′, 900 b′ and 900 c′ to alsorespectively receive the impulse radio signal 1402′ that passed over anindirect path 1406 a′, 1406 b′ and 1406 c′ between the transmittingimpulse radio unit 1000′ and the receiving impulse radio units 900 a′,900 b′ and 900 c′. Each receiving impulse radio unit 900 a′, 900 b′ and900 c′ receives both of these impulse radio signals 1402′ in addition toother reflected impulse radio signals 1402′ (not shown) over time andgenerates a second waveform 1504 a′, 1504 b′ and 1504 c′ (see FIG. 18b).Each second waveform 1504 a′, 1504 b′ and 1504 c′ is a time domainrepresentation of the actual distortion of the transmitted Gaussianwaveforms after being bounced of the intruder 1102′ and filtered by theenvironment around the transmitting impulse radio unit 1000′ and thereceiving impulse radio units 900 a′, 900 b′ and 900 c′. In other words,the second waveforms 1504 a′, 1504 b′ and 1504′ each correspond to thereceived impulse shapes of the impulse radio signals 1402′ that arereceived by each receiving impulse radio unit 900 a′, 900 b′ and 900 c′when the intruder 1102′ is located in the protection zone 1104′.

Each of the receiving impulse radio units 900 a′, 900 b′ and 900 c′includes a processor 1408′ that respectively compares the first waveform1502 a′, 1502 b′ and 1502 c′ and the second waveform 1504 a′, 1504 b′and 1504 c′ to determine whether there is a change between the firstwaveform 1502 a′, 1502 b′ and 1502 c′ and the second waveform 1504 a′,1504 b′ and 1504 c′ caused by an intruder 1102′ entering the protectionzone 1104′. To illustrate this change between waveforms reference ismade to FIGS. 18a and 18 b, where there are respectively illustratedexemplary first waveforms 1502 a′, 1502 b′, 1502 c′ and exemplary secondwaveforms 1504 a′, 1504 b′ and 1504 c′ that could be generated by thereceiving impulse radio units 900 a′, 900 b′ and 900 c′. For instance,the receiving impulse radio unit 900 a′ would generate the firstwaveform 1502 a′ and the second waveform 1504 a′. Each first waveform1502 a′, 1502 b′ and 1502 c′ has an initial wavefront 1503 a′, 1503 b′and 1503 c′ representative of the first received impulse radio pulses ofthe impulse radio signal 1402′. Likewise, each second waveform 1504 a′,1504 b′ and 1504 c′ has an initial wavefront 1506 a′, 1506 b′ and 1506c′ representative of the first received impulse radio pulses in thesubsequently received impulse radio signal 1402′. In addition, thesecond waveforms 1504 a′, 1504 b′ and 1504 c′ each have a multipathreflection part 1508 a′, 1508 b′ and 1508 c′ caused by the intruder1102′ that was absent in the first waveforms 1502 a′, 1502 b′ and 1502c′ but present in the second waveforms 1504 a′, 1504 b′ and 1504 c′.These multipath reflection parts 1508 a′, 1508 b′ and 1508 c′ are causedby the reception of the impulse radio signals 1402′ that bounced off theintruder 1102′ and passed over the indirect path 1406 a′, 1406 b′ and1406 c′ between the transmitting impulse radio unit 1000 and thereceiving impulse radio units 900 a′, 900 b′ and 900 c′. The distances“d1”, “d2” and “d3” which are the differences between the direct paths1402′ and indirect paths 1406 a′, 1406 b′ and 1406 c′ can be calculatedknowing the elapsed time “t1”, “t2” and “t3” between the initialwavefront 1506 a′, 1506 b′ and 1506 c′ and the multipath reflection part1508 a′, 1508 b′ and 1508 c′ of the second waveforms 1504 a′, 1504 b′and 1504 c′.

Again it should be understood that there may be many items (e.g., walls,trees, furniture . . . ) within the protection zone 1104′ that couldcause a multipath reflection part in the first waveform 1502 a′, 1502 b′and 1502 c′ and the second waveform 1504 a′, 1504 b′ and 1504 c′ but itis the difference between the two waveforms that indicates the presenceof one or more intruders 1102′. Moreover, it should be noted that theshape of the protection zone 1104′ in this embodiment is basicallyarbitrary as compared to the specially designed shape of the protectionzone 1104″ the third embodiment.

After calculating the distances “d1”, “d2” and “d3” which are thedifferences between the direct paths 1402′ and indirect paths 1406 a′,1406 b′ and 1406 c′, each receiving impulse radio unit 900 a′, 900 b′and 900 c′ and transmitting unit 1000′ forwards their calculateddistance “d1”, “d2” or “d3” to the transmitting impulse radio unit1000′. Thereafter, the transmitting impulse radio unit 1000′ has aprocessor 1802′ that use the distances “d1”, “d2” and “d3” and the knownpositions of the receiving impulse radio units 900 a′, 900 b′ and 900 c′to calculate the location of the intruder 1102′ within the protectionzone 1104′. Again, the position of intruder 1102′ can be determined bythe processor 1802′ using a numerical algorithm such as Newton-Raphsonmethod or some other techniques. Once the position and coordinates ofthe intruder 1102′ are determined, various filtering techniques (e.g.,Kalman filter) can be used by the intrusion detection system 1100′ totrack the movement of the intruder 1102′ within the protection zone1104′.

It should be understood that two receiving impulse radio units 900 a′and 900 b′ could be used to calculate the position of the intruder 1102′within the protection zone 1104′. This is possible in the situationwhere one of the three receiving impulse radio units 900 a′, 900 b′ or900 c′ can be eliminated if a part of the protection zone 1104′ is notrequired to be scanned and as such true triangulation of the position ofthe intruder 1102′ need not be performed.

Referring to FIGS. 19a-19 b, there is a flowchart illustrating the basicsteps of a second embodiment of the preferred method 1600′ of thepresent invention. Beginning at step 1902, the transmitting impulseradio unit 1000′ operates to transmit the impulse radio signal 1402′. Atthis time, the impulse radio signal 1402′ is made up of impulse radiopulses that are transmitted within and through a protection zone 1104′that does not have an intruder 1102′.

At step 1904, the first receiving impulse radio unit 900 a′ operates toreceive the impulse radio signal 1402′ and generate the first waveform1502 a′. Again, the first receiving impulse radio unit 900 a′ receivesthe impulse radio signal 1402′ and generates a first waveform 1502 a′(see FIG. 18a) that is a time domain representation of the actualdistortion of the transmitted Gaussian waveform after being filtered bythe environment around the transmitting impulse radio unit 1000′ and thereceiving impulse radio units 900 a′, 900 b′ and 900 c′. At this time,the first waveform 1502 a′ corresponds to the received impulse shape ofthe impulse radio signal 1402′ that is received by the first receivingimpulse radio unit 900 a′ when there is no intruder 1102′ located in theprotection zone 1104′.

At step 1906, the second receiving impulse radio unit 900 b′ operates toreceive the impulse radio signal 1402′ and generate the first waveform1502 b′. Again, the second receiving impulse radio unit 900 b′ receivesthe impulse radio signal 1402′ and generates a first waveform 1502 b′(see FIG. 18a) that is a time domain representation of the actualdistortion of the transmitted Gaussian waveform after being filtered bythe environment around the transmitting impulse radio unit 1000′ and thereceiving impulse radio units 900 a′, 900 b′ and 900 c′. At this time,the first waveform 1502 b′ corresponds to the received impulse shape ofthe impulse radio signal 1402′ that is received by the second receivingimpulse radio unit 900 b′ when there is no intruder 1102′ located in theprotection zone 1104′.

At step 1908, the third receiving impulse radio unit 900 c′ operates toreceive the impulse radio signal 1402′ and generate the first waveform1502 c′. Again, the third receiving impulse radio unit 900 c′ receivesthe impulse radio signal 1402′ and generates a first waveform 1502 c′(see FIG. 18a) that is a time domain representation of the actualdistortion of the transmitted Gaussian waveform after being filtered bythe environment around the transmitting impulse radio unit 1000′ and thereceiving impulse radio units 900 a′, 900 b′ and 900 c′. At this time,the first waveform 1502 c′ corresponds to the received impulse shape ofthe impulse radio signal 1402′ that is received by the third receivingimpulse radio unit 900 c′ when there is no intruder 1102′ located in theprotection zone 1104′. It should be understood that steps 1904, 1906 and1908 can take place in any order depending on the locations of thereceiving impulse radio units 900 a′, 900 b′ and 900 c′ with respect tothe location of the transmitting impulse radio unit 1000′.

At step 1910 and at a subsequent time with respect to step 1904, thefirst receiving impulse radio unit 900 a′ operates to receive theimpulse radio signal 1402′ and generate the second waveform 1504 a′. Inthe present example, the second waveform 1504 a′ (see FIG. 18b)illustrates what the impulse radio signals 1402′ received by the firstreceiving impulse radio unit 900 a′ looks like in the time domain withan intruder 1102′ located in the protection zone 1104′. In other words,the second waveform 1502 a′ corresponds to the received impulse shape ofthe impulse radio signals 1402′ that are received by the first receivingimpulse radio unit 900 a′ over the direct path 1404 a′ and the indirectpath 1406 a′ when the intruder 1102′ is located in the protection zone1104′.

At step 1912 and at a subsequent time with respect to step 1908, thesecond receiving impulse radio unit 900 b′ operates to receive theimpulse radio signal 1402′ and generate the second waveform 1504 b′. Inthe present example, the second waveform 1504 b′ (see FIG. 18b)illustrates what the impulse radio signals 1402′ received by the secondreceiving impulse radio unit 900 b′ looks like in the time domain withan intruder 1102′ located in the protection zone 1104′. In other words,the second waveform 1502 b′ corresponds to the received impulse shape ofthe impulse radio signals 1402′ that are received by the secondreceiving impulse radio unit 900 b′ over the direct path 1404 b′ and theindirect path 1406 b′ when the intruder 1102′ is located in theprotection zone 1104′.

At step 1914 and at a subsequent time with respect to step 2008, thethird receiving impulse radio unit 900 c′ operates to receive theimpulse radio signal 1402′ and generate the second waveform 1504 c′. Inthe present example, the second waveform 1504 c′ (see FIG. 18b)illustrates what the impulse radio signals 1402′ received by the thirdreceiving impulse radio unit 900 c′ looks like in the time domain withan intruder 1102′ located in the protection zone 1104′. In other words,the second waveform 1502 c′ corresponds to the received impulse shape ofthe impulse radio signals 1402′ that are received by the third receivingimpulse radio unit 900 c′ over the direct path 1404 c′ and the indirectpath 1406 c′ when the intruder 1102′ is located in the protection zone1104′. It should be understood that steps 1910, 1912 and 1914 can takeplace in any order depending on the locations of the receiving impulseradio units 900 a′, 900 b′ and 900 c′ with respect to the location ofthe transmitting impulse radio unit 1000′.

At step 1916, the processor 1408 a′ within the first receiving impulseradio unit 900 a′ operates to compare the first waveform 1502 a′ and thesecond waveform 1504 a′ to determine whether there is a change betweenthe first waveform 1502 a′ and the second waveform 1504 a′ caused by anintruder 1102′ entering the protection zone 1104′. In the presentexample, there is a change between the first waveform 1502 a′ and thesecond waveform 1504 a′ because an intruder 1102′ was not present whenthe first waveform 1502 a′ was generated but the intruder 1102′ waspresent when the second waveform 1504 a′ was generated by the firstreceiving impulse radio unit 900 a′ (see FIGS. 18a-18 b). This change isnoticeable due to the presence of the multipath reflection part 1508 a′caused by the intruder 1102′. Of course, the first receiving impulseradio unit 900 a′ may generate many second waveforms at step 1910 inwhich there is no difference or very little difference with a firstwaveform because an intruder 1102′ was not present. If an intruder 1102′is not present in the protection zone 1104′ then the method 1600′returns to and repeats steps 1910 and 1916 until an intruder 1102′ isdetermined to be present in the protection zone 1104′.

At step 1918, if the intruder 1102′ is determined to be in theprotection zone 1104′, the processor 1408 a′ could then calculate thedistance “d1” between direct and indirect paths by knowing the elapsedtime “t1” between the initial wavefront 1506 a′ and the multipathreflection part 1508 a′ of the second waveform 1504 a′ (see FIG. 18b).For instance, the distance “d1” can be calculated to be 0.984 feet foreach nanosecond in the elapsed time “t1” between the initial wavefront1506 a′ and the multipath reflection part 1508 a′ of the second waveform1504 a′ (see FIG. 18b).

At step 1920, the processor 1408 b′ within the second receiving impulseradio unit 900 b′ operates to compare the first waveform 1502 b′ and thesecond waveform 1504 b′ to determine whether there is a change betweenthe first waveform 1502 b′ and the second waveform 1504 b′ caused by anintruder 1102′ entering the protection zone 1104′. In the presentexample, there is a change between the first waveform 1502 b′ and thesecond waveform 1504 b′ because an intruder 1102′ was not present whenthe first waveform 1502 b′ was generated but the intruder 1102′ waspresent when the second waveform 1504 b′ was generated by the secondreceiving impulse radio unit 900 b′ (see FIGS. 18a-18 b). This change isnoticeable due to the presence of the multipath reflection part 1508 b′caused by the intruder 1102′. Of course, the second receiving impulseradio unit 900 b′ may generate many second waveforms at step 1912 inwhich there is no difference or very little difference with a firstwaveform because an intruder 1102′ was not present. If an intruder 1102′is not present in the protection zone 1104′ then the method 1600′returns to and repeats steps 1912 and 1920 until an intruder 1102′ isdetermined to be present in the protection zone 1104′.

At step 1922, if the intruder 1102′ is determined to be in theprotection zone 1104′, the processor 1408 b′ could then calculate thedistance “d2” between direct and indirect paths by knowing the elapsedtime “t2” between the initial wavefront 1506 b′ and the multipathreflection part 1508 b′ of the second waveform 1504 b′ (see FIG. 18b).For instance, the distance “d2” can be calculated to be 0.984 feet foreach nanosecond in the elapsed time “t2” between the initial wavefront1506 b′ and the multipath reflection part 1508 b′ of the second waveform1504 b′ (see FIG. 18b).

At step 1924, the processor 1408 c′ within the third receiving impulseradio unit 900 c′ operates to compare the first waveform 1502 c′ and thesecond waveform 1504 c′ to determine whether there is a change betweenthe first waveform 1502 c′ and the second waveform 1504 c′ caused by anintruder 1102′ entering the protection zone 1104′. In the presentexample, there is a change between the first waveform 1502 c′ and thesecond waveform 1504 c′ because an intruder 1102′ was not present whenthe first waveform 1502 c′ was generated but the intruder 1102′ waspresent when the second waveform 1504 c′ was generated by the thirdreceiving impulse radio unit 900 c′ (see FIGS. 18a-18 b). This change isnoticeable due to the presence of the multipath reflection part 1508 c′caused by the intruder 1102′. Of course, the third receiving impulseradio unit 900 c′ may generate many second waveforms at step 1914 inwhich there is no difference or very little difference with a firstwaveform because an intruder 1102′ was not present. If an intruder 1102′is not present in the protection zone 1104′ then the method 1600′returns to and repeats steps 1914 and 1924 until an intruder 1102′ isdetermined to be present in the protection zone 1104′.

At step 1926, if the intruder 1102′ is determined to be in theprotection zone 1104′, the processor 1408 c′ could then calculate thedistance “d3” between direct and indirect paths by knowing the elapsedtime “t3” between the initial wavefront 1506 c′ and the multipathreflection part 1508 c′ of the second waveform 1504 c′ (see FIG. 18b).For instance, the distance “d3” can be calculated to be 0.984 feet foreach nanosecond in the elapsed time “t3” between the initial wavefront1506 c′ and the multipath reflection part 1508 c′ of the second waveform1504 c′ (see FIG. 18b).

At step 1928, after calculating the distances “d1”, “d2” and “d3”between each receiving impulse radio unit 900 a′, 900 b′ and 900 c′ andthe intruder 1102′, each receiving impulse radio unit 900 a′, 900 b′ and900 c′ forwards their calculated distance “d1”, “d2” or “d3” to thetransmitting impulse radio unit 1000′.

At step 1930, the transmitting impulse radio unit 1000′ has a processor1802′ that use the distances “d1”, “d2” and “d3” and the known positionsof the receiving impulse radio units 900 a′, 900 b′ and 900 c′ tocalculate the location of the intruder 1102′ within the protection zone1104′. Again, the position of intruder 1102′ can be determined by theprocessor 1802′ using a numerical algorithm such as Newton-Raphsonmethod or some other techniques.

At step 1932, once the position and coordinates of the intruder 1102′are determined at step 1932, then various filtering techniques (e.g.,Kalman filter) can be used by the intrusion detection system 1100′ totrack the movement of the intruder 1102′ within the protection zone1104′.

At step 1934, the intrusion detection system 1100′ sounds an alarmand/or informs remote security personnel when there is an intruder 1102′present in the protection zone 1104′. For extra security, the intrusiondetection system 1100′ can use impulse radio technology to alert theremote security personnel.

Detailed Description of Third Embodiment

Referring to FIG. 20, there is a diagram illustrating a third embodimentof the intrusion detection system 1100 in accordance with the presentinvention. The third embodiment of the intrusion detection system 1100is illustrated using double prime referenced numbers. Basically, theintrusion detection system 1100″ is similar to the second embodimentexcept that prior to detecting any intruders 1102″ the intrusiondetection system 1100″ can utilize a test subject 2002″ and impulseradio technology to design the shape of the protection zone 1104″. Inother words, the intrusion detection system 1100″ enables the creationof an unusually shaped protection zone 1104 c″ instead of using thearbitrary shapes associated with the protection zones 1104 and 1104′ ofthe first two embodiments. Prior to arming the intrusion detectionsystem 1100′, the system can be put into a “learning mode”. During the“learning mode”, the test subject 2002″ traverses the perimeter 2204″ ofthe protection zone 1104 c″ to be protected and the intrusion detectionsystem 1100″ would track the test subject 2002″ and build a two andpossibly three-dimensional representation of the shape of the protectionzone 1104 c″. The intrusion detection system 1100″ can track the testsubject 2002″ in the same manner the intrusion detection system 1100′would track an intruder 1104′ in the second embodiment.

Like the second embodiment, the intrusion detection system 1100″includes a transmitting impulse radio unit 1000″ and at least threereceiving impulse radio units 900 a″, 900 b″ and 900 c″. Thetransmitting impulse radio unit 1000″ transmits an impulse radio signal1402″ having a known pseudorandom sequence of pulses that look like aseries of Gaussian waveforms (see FIG. 1). Initially, the impulse radiosignal 1402″ is transmitted within and through an area including theprotection zone 1104 c″ that does not have an intruder 1102″.

Each receiving impulse radio unit 900 a″, 900 b″ and 900 c″ receives thefirst impulse radio signal 1402″ and generates a first waveform 1502 a″,1502 b″ and 1502 c″ (similar to the first waveforms 1502 a′, 1502 b′ and1502 c′ shown in FIG. 18a). Each of the first waveforms 1502 a″, 1502 b″and 1502 c″ is a time domain representation of the actual distortion ofthe transmitted Gaussian waveform after being filtered by theenvironment around the transmitting impulse radio unit 1000″ and eachreceiving impulse radio unit 900 a″, 900 b″ and 900 c″. In other words,each first waveform 1502 a″, 1502 b″ and 1502 c″ corresponds to thereceived impulse shape of the impulse radio signal 1402″ that isreceived by each receiving impulse radio unit 900 a″, 900 b″ and 900 c″when there is no intruder 1102″ located in or near the protection zone1104 c″.

After the generation of the first waveforms 1502 a″, 1502 b″ and 1502c″, each receiving impulse radio unit 900 a″, 900 b″ and 900 c″ receivesat a subsequent time “ts” the impulse radio signal 1402″ having a knownpseudorandom sequence of pulses that are similar to the pulses initiallytransmitted by the transmitting impulse radio unit 1000″ during thegeneration of the first waveforms 1502 a″, 1502 b″ and 1502 c″. Howeverat this time, the impulse radio signal 1402″ is transmitted within andthrough a protection zone 1104 c″ that does have an intruder 1102″ in ornear it.

In particular, each receiving impulse radio unit 900 a″, 900 b″ and 900c″ respectively receives the impulse radio signal 1402″ that passed overa direct path 1404 a″, 1404 b″ and 1404 c″ between the transmittingimpulse radio unit 1000″ and the receiving impulse radio unit 900 a″,900 b″ and 900 c″. The presence of the intruder 1102″ causes eachreceiving impulse radio unit 900 a″, 900 b″ and 900 c″ to alsorespectively receive the impulse radio signal 1402″ that passed over anindirect path 1406 a″, 1406 b″ and 1406 c″ from the transmitting impulseradio unit 1000″ to the receiving impulse radio unit 900 a″, 900 b″ and900 c″. Each receiving impulse radio unit 900 a″, 900 b″ and 900 c″receives both of these impulse radio signals 1402″ in addition to otherreflected impulse radio signals 1402″ (not shown) over time andgenerates a second waveform 1504 a″, 1504 b″ and 1504 c″ (similar to thesecond waveforms 1504 a′, 1504 b′ and 1504 c′ shown in FIG. 18b). Eachsecond waveform 1504 a″, 1504 b″ and 1504 c″ is a time domainrepresentation of the actual distortion of the transmitted Gaussianwaveforms after being bounced of the intruder 1102″ and filtered by theenvironment around the transmitting impulse radio unit 1000″ and thereceiving impulse radio units 900 a″, 900 b″ and 900 c″. In other words,the second waveforms 1504 a″, 1504 b″ and 1504 c″ each correspond to thereceived impulse shapes of the impulse radio signals 1402″ that arereceived by each receiving impulse radio unit 900 a″, 900 b″ and 900 c″when the intruder 1102″ is located in or near the protection zone 1104c″. A determination as to whether the intruder 1104″ is actually insidethe specially shaped protection zone 1104 c″ is made later by theprocessor 1802″ associated with the transmitting impulse radio unit1000″.

Each of the receiving impulse radio units 900 a″, 900 b″ and 900 c″includes a processor 1408″ that compares the first waveform 1502 a″,1502 b″ and 1502 c″ and the second waveform 1504 a″, 1504 b″ and 1504 c″to determine whether there is a change between the first waveform 1502a″, 1502 b″ and 1502 c″ and the second waveform 1504 a″, 1504 b″ and1504 c″ caused by an intruder 1102″ entering or coming near theprotection zone 1104 c″. Like the first waveforms 1502 a′, 1502 b′ and1502 c′ and the second waveforms 1504 a′, 1504 b′ and 1504 c′ shown inFIGS. 19a and 19 b, each first waveform 1502 a″, 1502 b″ and 1502 c″ hasan initial wavefront 1503 a″, 1503 b″ and 1503 c″ representative of thefirst received impulse radio pulses of the impulse radio signal 1402″.Likewise, each second waveform 1504 a″, 1504 b″ and 1504 c″ has aninitial wavefront 1506 a″, 1506 b″ and 1506 c″ representative of thefirst received impulse radio pulses in the subsequently received impulseradio signal 1402″. In addition, the second waveforms 1504 a″, 1504 b″and 1504 c″ each have a multipath reflection part 1508 a″, 1508 b″ and1508 c″ caused by the intruder 1102″ that was absent in the firstwaveforms 1502 a″, 1502 b″ and 1502 c″ but present in the secondwaveforms 1504 a″, 1504 b″ and 1504 c″. These multipath reflection parts1508 a″, 1508 b″ and 1508 c″ are caused by the reception of the impulseradio signals 1402″ that bounced off the intruder 1102″ and passed overthe indirect path 1406 a″, 1406 b″ and 1406 c″ between the transmittingimpulse radio unit 1000″ and the receiving impulse radio units 900 a″,900 b″ and 900 c″. The distances “d1”, “d2” and “d3” between direct andindirect paths can be calculated knowing the elapsed time “t1”, “t2” and“t3” between the initial wavefront 1506 a″, 1506 b″ and 1506 c″ of thesecond waveforms 1504 a″, 1504 b″ and 1504 c″ and the multipathreflection part 1508 a″, 1508 b″ and 1508 c″. Again, a determination asto whether the intruder 1104″ is actually inside the specially shapedprotection zone 1104 c″ is made later by the processor 1802″ associatedwith the transmitting impulse radio unit 1000″.

It should be understood that there may be many items (e.g., walls,trees, furniture . . . ) within or near the protection zone 1104 c″ thatcould cause a multipath reflection part in the first waveform 1502 a″,1502 b″ and 1502 c″ and the second waveforms 1504 a″, 1504 b″ and 1504c″ but it is the difference between the two waveforms that indicates thepresence of one or more intruders 1102″.

After calculating the distances “d1”, “d2” and “d3” between direct andindirect paths, each receiving impulse radio unit 900 a″, 900 b″ and 900c″ forwards their calculated distance “d1”, “d2” or “d3” to thetransmitting impulse radio unit 1000″. Thereafter, the transmittingimpulse radio unit 1000″ has a processor 1802″ that use the distances“d1”, “d2” and “d3” and the known positions of the receiving impulseradio units 900 a″, 900 b″ and 900 c″ to calculate the location withinor near the protection zone 1104 c″ of the intruder 1102″.

To do determine whether the intruder 1102″ is actually within theprotection zone 1104 c″ (as shown) or just near the protection zone 1104c″, the processor 1802″ would determine the location of the intruder1102″ and then compare this location to the two and possiblythree-dimensional representation of the shape of the protection zone1104 c″. Again, the position of intruder 1102″ can be determined by theprocessor 1802″ using a numerical algorithm such as Newton-Raphsonmethod or some other techniques. Once the position and coordinates ofthe intruder 1102″ are determined, various filtering techniques (e.g.,Kalman filter) can be used by the intrusion detection system 1100″ totrack the movement of the intruder 1102″ within the protection zone 1104c″.

Referring to FIGS. 21a-21 b, there is a flowchart illustrating the basicsteps of a third embodiment of the preferred method 1600″ of the presentinvention. Beginning at step 2101, prior to arming the intrusiondetection system 1100″, the system is put into a “learning mode”. Duringthe “learning mode”, the test subject 2002″ traverses the perimeter2204″ of the protection zone 1104 c″ to be protected and the intrusiondetection system 1100″ would track the test subject 2002″ and build atwo and possibly three-dimensional representation of the shape of theprotection zone 1104 c″. The intrusion detection system 1100″ can trackthe test subject 2002″ in the same manner the intrusion detection system1100′ would track an intruder 1104′ in the second embodiment.

At step 2102, after creating the shape of the protection zone 1104 c″,the transmitting impulse radio unit 1000″ operates to transmit theimpulse radio signal 1402″. At this time, the impulse radio signal 1402″is made up of impulse radio pulses that are transmitted within andthrough a protection zone 1104 c″ that does not have an intruder 1102″.

At step 2104, the first receiving impulse radio unit 900 a″ operates toreceive the impulse radio signal 1402″ and generate the first waveform1502 a″. Again, the first receiving impulse radio unit 900 a″ receivesthe impulse radio signal 1402″ and generates a first waveform 1502 a″(e.g., see first waveform 1502 a′ in FIG. 19a) that is a time domainrepresentation of the actual distortion of the transmitted Gaussianwaveform after being filtered by the environment around the transmittingimpulse radio unit 1000″ and the receiving impulse radio units 900 a″,900 b″ and 900 c″. At this time, the first waveform 1502 a″ correspondsto the received impulse shape of the impulse radio signal 1402″ that isreceived by the first receiving impulse radio unit 900 a″ when there isno intruder 1102″ located in or near the protection zone 1104 c″.

At step 2106, the second receiving impulse radio unit 900 b″ operates toreceive the impulse radio signal 1402″ and generate the first waveform1502 b″. Again, the second receiving impulse radio unit 900 b″ receivesthe impulse radio signal 1402″ and generates a first waveform 1502 b″(e.g., see first waveform 1502 b′ in FIG. 18a) that is a time domainrepresentation of the actual distortion of the transmitted Gaussianwaveform after being filtered by the environment around the transmittingimpulse radio unit 1000″ and the receiving impulse radio units 900 a″,900 b″ and 900 c″. At this time, the first waveform 1502 b″ correspondsto the received impulse shape of the impulse radio signal 1402″ that isreceived by the second receiving impulse radio unit 900 b″ when there isno intruder 1102″ located in or near the protection zone 1104 c″.

At step 2108, the third receiving impulse radio unit 900 c″ operates toreceive the impulse radio signal 1402″ and generate the first waveform1502 c″. Again, the third receiving impulse radio unit 900 c″ receivesthe impulse radio signal 1402″ and generates a first waveform 1502 c″(e.g., see first waveform 1502 c′ in FIG. 18a) that is a time domainrepresentation of the actual distortion of the transmitted Gaussianwaveform after being filtered by the environment around the transmittingimpulse radio unit 1000″ and the receiving impulse radio units 900 a″,900 b″ and 900 c″. At this time, the first waveform 1502 c″ correspondsto the received impulse shape of the impulse radio signal 1402″ that isreceived by the third receiving impulse radio unit 900 c″ when there isno intruder 1102″ located in or near the protection zone 1104 c″. Itshould be understood that steps 2104, 2106 and 2108 can take place inany order depending on the locations of the receiving impulse radiounits 900 a″, 900 b″ and 900 c″ with respect to the location of thetransmitting impulse radio unit 1000″.

At step 2110 and at a subsequent time with respect to step 2304, thefirst receiving impulse radio unit 900 a″ operates to receive theimpulse radio signal 1402″ and generate the second waveform 1504 a″. Inthe present example, the second waveform 1504 a″ (e.g., see secondwaveform 1504 a′ in FIG. 18b) illustrates what the impulse radio signals1402″ received by the first receiving impulse radio unit 900 a″ lookslike in the time domain with an intruder 1102″ located in or near theprotection zone 1104 c″. In other words, the second waveform 1502 a″corresponds to the received impulse shape of the impulse radio signals1402″ that are received by the first receiving impulse radio unit 900 a″over the direct path 1404 a″ and the indirect path 1406 a″ when theintruder 1102″ is located in or near the protection zone 1104 c″. Adetermination as to whether the intruder 1104″ is actually inside thespecially shaped protection zone 1104 c″ is made later at step 2030 bythe processor 1802″ associated with the transmitting impulse radio unit1000″.

At step 2112 and at a subsequent time with respect to step 2308, thesecond receiving impulse radio unit 900 b″ operates to receive theimpulse radio signal 1402″ and generate the second waveform 1504 b″. Inthe present example, the second waveform 1504 b″ (e.g., see secondwaveform 1504 b′ in FIG. 18b) illustrates what the impulse radio signals1402″ received by the second receiving impulse radio unit 900 b″ lookslike in the time domain with an intruder 1102″ located in or near theprotection zone 1104 c″. In other words, the second waveform 1502 b″corresponds to the received impulse shape of the impulse radio signals1402″ that are received by the second receiving impulse radio unit 900b″ over the direct path 1404 b″ and the indirect path 1406 b″ when theintruder 1102″ is located in or near the protection zone 1104 c″. Again,a determination as to whether the intruder 1104″ is actually inside thespecially shaped protection zone 1104 c″ is made later at step 2130 bythe processor 1802″ associated with the transmitting impulse radio unit1000″.

At step 2114 and at a subsequent time with respect to step 2108, thethird receiving impulse radio unit 900 c″ operates to receive theimpulse radio signal 1402″ and generate the second waveform 1504 c″. Inthe present example, the second waveform 1504 c″ (e.g., see secondwaveform 1504 c′ in FIG. 18b) illustrates what the impulse radio signals1402″ received by the third receiving impulse radio unit 900 c″ lookslike in the time domain with an intruder 1102″ located in or near theprotection zone 1104 c″. In other words, the second waveform 1502 c″corresponds to the received impulse shape of the impulse radio signals1402″ that are received by the third receiving impulse radio unit 900 c″over the direct path 1404 c″ and the indirect path 1406 c″ when theintruder 1102″ is located in or near the protection zone 1104 c″. Again,a determination as to whether the intruder 1104″ is actually inside thespecially shaped protection zone 1104 c′ is made later at step 2030 bythe processor 1802″ associated with the transmitting impulse radio unit1000″. It should be understood that steps 2110, 2112 and 2114 can takeplace in any order depending on the locations of the receiving impulseradio units 900 a″, 900 b″ and 900 c″ with respect to the location ofthe transmitting impulse radio unit 1000″.

At step 2116, the processor 1408 a″ within the first receiving impulseradio unit 900 a″ operates to compare the first waveform 1502 a″ and thesecond waveform 1504 a″ to determine whether there is a change betweenthe first waveform 1502 a″ and the second waveform 1504 a″ caused by anintruder 1102″ coming near or entering the protection zone 1104 c″. Inthe present example, there is a change between the first waveform 1502a″ and the second waveform 1504 a″ because an intruder 1102″ was notpresent when the first waveform 1502 a″ was generated but the intruder1102″ was present when the second waveform 1504 a″ was generated by thefirst receiving impulse radio unit 900 a″ (e.g., see first waveform 1502a′ and second waveform 1504 a′ in FIGS. 18a-18 b). This change isnoticeable due to the presence of the multipath reflection part 1508 a″caused by the intruder 1102″. Of course, the first receiving impulseradio unit 900 a″ may generate many second waveforms at step 2110 inwhich there is no difference or very little difference with a firstwaveform because an intruder 1102″ was not present. If an intruder 1102″is not within or near the protection zone 1104 c″ then the method 1600″returns to and repeats steps 2110 and 2116 until an intruder 1102″ isdetermined to be within or near the protection zone 1104 c″.

At step 2118, if the intruder 1102″ is determined to be within or nearthe protection zone 1104 c″, the processor 1408 a″ could then calculatethe distance “d1” between direct and indirect paths by knowing theelapsed time “t1” between the initial wavefront 1506 a″ and themultipath reflection part 1508 a″ of the second waveform 1504 a″ (e.g.,see second waveform 1504 a′ in FIG. 18b). For instance, the distance“d1” can be calculated to be 0.984 feet for each nanosecond in theelapsed time “t1” between the initial wavefront 1506 a″ and themultipath reflection part 1508 a″ of the second waveform 1504 a″ (e.g.,see second waveform 1504 a′ in FIG. 18b). Again, a determination as towhether the intruder 1104″ is actually inside the specially shapedprotection zone 1104 c″ is made later at step 2130 by the processor1802″ associated with the transmitting impulse radio unit 1000″.

At step 2120, the processor 1408 b″ within the second receiving impulseradio unit 900 b″ operates to compare the first waveform 1502 b″ and thesecond waveform 1504 b″ to determine whether there is a change betweenthe first waveform 1502 b″ and the second waveform 1504 b″ caused by anintruder 1102″ coming near or entering the protection zone 1104 c″. Inthe present example, there is a change between the first waveform 1502b″ and the second waveform 1504 b″ because an intruder 1102″ was notpresent when the first waveform 1502 b″ was generated but the intruder1102″ was present when the second waveform 1504 b″ was generated by thesecond receiving impulse radio unit 900 b″ (e.g., see first waveform1502 b′ and second waveform 1504 b′ in FIGS. 18a-18 b). This change isnoticeable due to the presence of the multipath reflection part 1508 b″caused by the intruder 1102″. Of course, the second receiving impulseradio unit 900 b″ may generate many second waveforms at step 2112 inwhich there is no difference or very little difference with a firstwaveform because an intruder 1102″ was not present. If an intruder 1102″is not within or near the protection zone 1104 c″ then the method 1600″returns to and repeats steps 2112 and 2120 until an intruder 1102″ isdetermined to be within or near the protection zone 1104 c″.

At step 2122, if the intruder 1102″ is determined to be within or nearthe protection zone 1104 c″, the processor 1408 b″ could then calculatethe distance “d2” between direct and indirect paths by knowing theelapsed time “t2” between the initial wavefront 1506 b″ and themultipath reflection part 1508 b″ of the second waveform 1504 b″ (e.g.,see second waveform 1504 b′ in FIG. 18b). For instance, the distance“d2” can be calculated to be 0.984 feet for each nanosecond in theelapsed time “t2” between the initial wavefront 1506 b″ and themultipath reflection part 1508 b″ of the second waveform 1504 b″ (e.g.,see second waveform 1504 b′ in FIG. 18b). Again, a determination as towhether the intruder 1104″ is actually inside the specially shapedprotection zone 1104 c″ is made later at step 2030 by the processor1802″ associated with the transmitting impulse radio unit 1000″.

At step 2124, the processor 1408 c″ within the third receiving impulseradio unit 900 c″ operates to compare the first waveform 1502 c″ and thesecond waveform 1504 c″ to determine whether there is a change betweenthe first waveform 1502 c″ and the second waveform 1504 c″ caused by anintruder 1102″ coming near or entering the protection zone 1104 c″. Inthe present example, there is a change between the first waveform 1502c″ and the second waveform 1504 c″ because an intruder 1102″ was notpresent when the first waveform 1502 c″ was generated but the intruder1102″ was present when the second waveform 1504 c″ was generated by thethird receiving impulse radio unit 900 c″ (e.g., see first waveform 1502c′ and second waveform 1504 c′ in FIGS. 18a-18 b). This change isnoticeable due to the presence of the multipath reflection part 1508 c″caused by the intruder 1102″. Of course, the third receiving impulseradio unit 900 c″ may generate many second waveforms at step 2314 inwhich there is no difference or very little difference with a firstwaveform because an intruder 1102″ was not present. If an intruder 1102″is not within or near the protection zone 1104 c″ then the method 1600″returns to and repeats steps 2114 and 2124 until an intruder 1102″ isdetermined to be within or near the protection zone 1104 c″.

At step 2126, if the intruder 1102″ is determined to be within or nearthe protection zone 1104 c″, the processor 1408 c″ could then calculatethe distance “d3” between direct and indirect paths by knowing theelapsed time “t3” between the initial wavefront 1506 c″ and themultipath reflection part 1508 c″ of the second waveform 1504 c″ (e.g.,see second waveform 1504 c′ in FIG. 18b). For instance, the distance“d3” can be calculated to be 0.984 feet for each nanosecond in theelapsed time “t3” between the initial wavefront 1506 c″ and themultipath reflection part 1508 c″ of the second waveform 1504 c″ (e.g.,see second waveform 1504 c′ in FIG. 18b). Again, a determination as towhether the intruder 1104″ is actually inside the specially shapedprotection zone 1104 c″ is made later at step 2030 by the processor1802″ associated with the transmitting impulse radio unit 1000″.

At step 2128, after calculating the distances “d1”, “d2” and “d3”between direct and indirect paths, each receiving impulse radio unit 900a″, 900 b″ and 900 c″ forwards their calculated distance “d1”, “d2” or“d3” to the transmitting impulse radio unit 1000″.

At step 2130, the transmitting impulse radio unit 1000″ has a processor1802″ that use the distances “d1”, “d2” and “d3” and the known positionsof the receiving impulse radio units 900 a″, 900 b″ and 900 c″ tocalculate the location of the intruder 1102″ within or near theprotection zone 1104 c″. To determine whether the intruder 1102′ isactually within the protection zone 1104 c″ or just near the protectionzone 1104 c″, the processor 1802″ would determine the location of theintruder 1102″ and then compare this location to the two and possiblythree-dimensional representation of the shape of the protection zone1104 c″. Again, the position of intruder 1102″ can be determined by theprocessor 1802″ using a numerical algorithm such as Newton-Raphsonmethod or some other techniques.

At step 2132, once the position and coordinates of the intruder 1102″are determined at step 2130, then various filtering techniques (e.g.,Kalman filter) can be used by the intrusion detection system 1100″ totrack the movement of the intruder 1102″ within the protection zone 1104c″.

At step 2134, the intrusion detection system 1100″ sounds an alarmand/or informs remote security personnel when there is an intruder 1102″located within (or near) the protection zone 1104 c″. For extrasecurity, the intrusion detection system 1100″ can use impulse radiotechnology to alert the remote security personnel.

Referring to FIG. 22, there is illustrated a diagram of the intrusiondetection system 1100, 1100′ and 1100″ that uses one or more directiveantennas 2202. As shown, the transmitting impulse radio unit 1000, 1000′and 1000″ (only one shown) can use the directive antenna 2202 (only oneshown) to transmit the impulse radio signal in a predetermined directionsuch that radar is sensitive in a particular area 2204 (see solid line)and not sensitive in another area 2206 (see dashed line). In particular,the intrusion detection system 1100, 1100′ and 1100″ that uses andirective antenna 2202 can make the radar sensitive in a particular area2204 to detect a person 2208 or a dangerous animal 2210 that is notsupposed to be located in that area 2204 and at the same time thedirective antenna 2202 does not make the radar sensitive in another area2206 in which the dangerous animal 2210 is suppose to be located. Itshould be understood that the directive antenna 2202 can take manydifferent forms including, for example, a 180° directive antenna and a90° directive antenna. Moreover, it should also be understood that adirectional antenna 2202 could be placed at the receiving impulse radiounit 900, 900′ and 900″ or at both the receiving and transmittingimpulse radio units.

From the foregoing, it can be readily appreciated by those skilled inthe art that the present invention provides an intrusion detectionsystem and method that can utilize impulse radio technology to detectwhen an intruder has entered a protection zone. In addition, theintrusion detection system and method can utilize impulse radiotechnology to determine a location of the intruder within the protectionzone and also to track the movement of the intruder within theprotection zone. Moreover, the intrusion detection system and method canutilize impulse radio technology to create a specially shaped protectionzone before trying to detect when and where the intruder has penetratedand moved within the protection zone. There are many possibleapplications for using the present invention such as setting-up asecurity screen in a home/apartment (or just certain rooms in thehome/apartment), setting-up a security screen around a swimming pool . .. .

Although various embodiments of the present invention have beenillustrated in the accompanying Drawings and described in the foregoingDetailed Description, it should be understood that the invention is notlimited to the embodiments disclosed, but is capable of numerousrearrangements, modifications and substitutions without departing fromthe spirit of the invention as set forth and defined by the followingclaims.

What is claimed is:
 1. A method of intrusion detection, comprising:transmitting a first impulse radio signal from a first location;receiving the first impulse radio signal at a second location, saidsecond location being separate from said first location, said firstlocation and said second location associated with a protection zone;generating a first waveform which is a time domain representation of thereceived first impulse radio signal that indicates a multipath structureof a propagation channel of the transmitted first impulse radio signal;transmitting a second impulse radio signal from the first location;receiving the second impulse radio signal at the second location;generating a second waveform which is a time domain representation ofthe received second impulse radio signal that indicates a multipathstructure of a propagation channel of the transmitted second impulseradio signal; and comparing the first waveform and the second waveformto determine whether there is a change between the first waveform andthe second waveform indicative of an intruder entering the protectionzone.
 2. The method of claim 1, wherein said change between the firstwaveform and the second waveform is a multipath reflection part causedby the intruder.
 3. The method of claim 1, further comprising the stepsof: receiving at least one of the first impulse radio signal and thesecond impulse radio signal at a third location and a fourth location,said third and fourth locations being separate from each other and saidfirst and second locations; determining a position of the intruderwithin the protection zone.
 4. The method of claim 3, further comprisingthe step of: creating a shape of the protection zone by determining acurrent position of a test subject and tracking the movement of the testsubject to outline the shape of the protection zone by repeating thetransmitting, receiving, generating and comparing steps needed todetermine the position of the intruder but instead to track the testsubject so as to create the shape of the protection zone.
 5. A method ofintrusion detection, comprising: generating a first waveform which is atime domain representation of a received first impulse radio signal thatindicates a multipath structure of a propagation channel of atransmitted first impulse radio signal; generating a second waveformwhich is a time domain representation of a received second impulse radiosignal that indicates a multipath structure of a propagation channel ofa transmitted second impulse radio signal; and comparing the firstwaveform and the second waveform to determine whether there is a changebetween the first waveform and the second waveform indicative of anintruder entering a protection zone.
 6. The method of claim 5, whereinsaid change between the first waveform and the second waveform is amultipath reflection part caused by the intruder.
 7. The method of claim5, further comprising the steps of: receiving at least one of the firstimpulse radio signal and the second impulse radio signal at two or moreimpulse radio receivers; and determining a position of the intruderwithin the protection zone, wherein the steps of generating a firstwaveform, generating a second waveform, and comparing said firstwaveform and second waveform are performed at another impulse radioreceiver.
 8. The method of claim 7, further comprising the step of:creating a shape of the protection zone by determining a currentposition of a test subject and tracking the movement of the test subjectto outline the shape of the protection zone by repeating the generatingand comparing steps needed to determine the position of the intruder butinstead to track the test subject so as to create the shape of theprotection zone.
 9. A method of intrusion detection, comprising:transmitting a plurality of impulse radio signals from a first location;receiving the plurality of impulse radio signals at a second location,the second location being separate from the first location; generating aplurality of waveforms, each of the plurality of waveforms being timedomain representations of one of the plurality of impulse radio signalsreceived at the second location that indicates a multipath structure ofa propagation channel of the corresponding one of the transmittedplurality of impulse radio signals; and comparing two of said pluralityof waveforms to determine whether there is a difference between the twoof said plurality of waveforms that is indicative of an intruderentering a protection zone.
 10. The method of claim 9, wherein saidchange between the two of said plurality of waveforms is a multipathreflection part caused by the intruder.
 11. The method of claim 9,further comprising the steps of: receiving the plurality of impulseradio signals at a third location, the third location being separatefrom the first and second locations; receiving the plurality of impulseradio signals at a fourth location, the fourth location being separatefrom the first, second, and third locations; determining a position ofthe intruder within the protection zone.
 12. The method of claim 11,further comprising the step of: creating a shape of the protection zoneby determining a current position of a test subject and tracking themovement of the test subject to outline the shape of the protection zoneby repeating the transmitting, receiving, generating and comparing stepsneeded to determine the position of the intruder but instead to trackthe test subject so as to create the shape of the protection zone.
 13. Asecurity system comprising: a transmitting impulse radio unit fortransmitting a first impulse radio signal and a second impulse radiosignal from a first location; a receiving impulse radio unit forreceiving the first impulse radio signal and the second impulse radiosignal at a second location, said second location being separate fromsaid first location, said first location and said second locationassociated with a protection zone; said receiving impulse radio unit forgenerating a first waveform which is a time domain representation of thereceived first impulse radio signal that indicates a multipath structureof a propagation channel of the transmitted first impulse radio signal;said receiving impulse radio unit for generating a second waveform whichis a time domain representation of the received second impulse radiosignal that indicates a multipath structure of a propagation channel ofthe transmitted second impulse radio signal; and a processor forcomparing the first waveform to the second waveform to determine whetherthere is a change between the first waveform and the second waveformcaused by an intruder entering a protection zone.
 14. The securitysystem of claim 13, wherein said first impulse radio signal and thesecond impulse radio signals have the same form but they are transmittedat different times.
 15. The security system of claim 13, wherein saidchange between the first waveform and the second waveform is a multipathreflection part caused by the intruder that was absent in the firstwaveform but present in the second waveform.
 16. The security system ofclaim 13, further comprising at least two more receiving impulse radiounits located in different locations the presence of which enables acurrent position of the intruder to be determined within the protectionzone.
 17. The security system of claim 16, wherein said transmittingimpulse radio unit is capable of interacting with each of the receivingimpulse radio units to track the movement of a test subject so as tocreate a shape of the protection zone.
 18. The security system of claim13, wherein said receiving impulse radio unit is an ultra-widebandscanning receiver.
 19. An intrusion detection system comprising: aprocessor for generating a first waveform which is a time domainrepresentation of a received first impulse radio signal that indicates amultipath structure of a propagation channel of a transmitted firstimpulse radio signal; said processor for generating a second waveformwhich is a time domain representation of a received second impulse radiosignal that indicates a multipath structure of a propagation channel ofa transmitted second impulse radio signal; and said processor forcomparing the first waveform and the second waveform to determinewhether there is a change between the first waveform and the secondwaveform indicative of an intruder entering a protection zone.
 20. Theintrusion detection system of claim 19, wherein said change between thefirst waveform and the second waveform is a multipath reflection partcaused by the intruder.
 21. The intrusion detection system of claim 19,wherein: receiving at least one of the transmitted first impulse radiosignal and the transmitted second impulse radio signal at two or moreimpulse radio receivers; and determining a position of the intruderwithin the protection zone, wherein another impulse radio receiverincludes said processor.
 22. The intrusion detection system of claim 21,wherein said processor for creating a shape of the protection zone bydetermining a current position of a test subject and tracking themovement of the test subject to outline the shape of the protection zoneby repeating the generating and comparing steps needed to determine theposition of the intruder but instead to track the test subject so as tocreate the shape of the protection zone.
 23. A security systemcomprising: a transmitting impulse radio unit for transmitting aplurality of impulse radio signals from a first location; a firstreceiving impulse radio unit for receiving the plurality of impulseradio signals at a second location, the second location being separatefrom the first location; a processor for generating a plurality ofwaveforms, each of the plurality of waveforms being time domainrepresentations of one of the plurality of impulse radio signalsreceived at the second location that indicates a multipath structure ofa propagation channel of the corresponding one of the transmittedplurality of impulse radio signals; and said processor for comparing twoof said plurality of waveforms to determine whether there is adifference between the two of said plurality of waveforms that isindicative of an intruder entering a protection zone.
 24. The securitysystem of claim 23, wherein said change between the two of saidplurality of waveforms is a multipath reflection part caused by theintruder.
 25. The security system of claim 23, further comprising: asecond receiving impulse radio unit for receiving the plurality ofimpulse radio signals at a third location, the third location beingseparate from the first and second locations; a third receiving impulseradio unit for receiving the plurality of impulse radio signals at afourth location, the fourth location being separate from the first,second, and third locations; and said processor for determining aposition of the intruder within the protection zone.
 26. The securitysystem of claim 25, wherein said processor for creating a shape of theprotection zone by determining a current position of a test subject andtracking the movement of the test subject to outline the shape of theprotection zone by repeating the transmitting, receiving, generating andcomparing steps needed to determine the position of the intruder butinstead to track the test subject so as to create the shape of theprotection zone.
 27. The security system of claim 23, wherein said firstreceiving impulse radio unit is an ultra-wideband scanning receiver.